Add all unstable features to Unstable Book.

Add all unstable features to the Unstable Book, also remove a few that
either no longer exist or were promoted to stable.

These changes were extracted out of
rust-lang#40694

Author: frewsxcv

src/doc/unstable-book/src/SUMMARY.md

@@ -7,90 +7,207 @@
 - [abi_vectorcall](abi-vectorcall.md)
 - [abi_x86_interrupt](abi-x86-interrupt.md)
 - [advanced_slice_patterns](advanced-slice-patterns.md)
+- [alloc](alloc.md)
 - [alloc_jemalloc](alloc-jemalloc.md)
 - [alloc_system](alloc-system.md)
 - [allocator](allocator.md)
 - [allow_internal_unstable](allow-internal-unstable.md)
+- [as_unsafe_cell](as-unsafe-cell.md)
+- [ascii_ctype](ascii-ctype.md)
 - [asm](asm.md)
 - [associated_consts](associated-consts.md)
 - [associated_type_defaults](associated-type-defaults.md)
 - [attr_literals](attr-literals.md)
+- [binary_heap_extras](binary-heap-extras.md)
+- [binary_heap_peek_mut_pop](binary-heap-peek-mut-pop.md)
+- [borrow_state](borrow-state.md)
+- [box_heap](box-heap.md)
 - [box_patterns](box-patterns.md)
 - [box_syntax](box-syntax.md)
+- [c_void_variant](c-void-variant.md)
+- [catch_expr](catch-expr.md)
 - [cfg_target_feature](cfg-target-feature.md)
 - [cfg_target_has_atomic](cfg-target-has-atomic.md)
 - [cfg_target_thread_local](cfg-target-thread-local.md)
 - [cfg_target_vendor](cfg-target-vendor.md)
+- [char_escape_debug](char-escape-debug.md)
+- [closure_to_fn_coercion](closure-to-fn-coercion.md)
+- [coerce_unsized](coerce-unsized.md)
+- [collection_placement](collection-placement.md)
+- [collections](collections.md)
+- [collections_range](collections-range.md)
+- [command_envs](command-envs.md)
 - [compiler_builtins](compiler-builtins.md)
+- [compiler_builtins_lib](compiler-builtins-lib.md)
 - [concat_idents](concat-idents.md)
+- [concat_idents_macro](concat-idents-macro.md)
 - [conservative_impl_trait](conservative-impl-trait.md)
 - [const_fn](const-fn.md)
 - [const_indexing](const-indexing.md)
+- [core_char_ext](core-char-ext.md)
+- [core_float](core-float.md)
+- [core_intrinsics](core-intrinsics.md)
+- [core_panic](core-panic.md)
+- [core_private_bignum](core-private-bignum.md)
+- [core_private_diy_float](core-private-diy-float.md)
+- [core_slice_ext](core-slice-ext.md)
+- [core_str_ext](core-str-ext.md)
 - [custom_attribute](custom-attribute.md)
 - [custom_derive](custom-derive.md)
+- [dec2flt](dec2flt.md)
+- [decode_utf8](decode-utf8.md)
 - [default_type_parameter_fallback](default-type-parameter-fallback.md)
+- [derive_clone_copy](derive-clone-copy.md)
+- [derive_eq](derive-eq.md)
+- [discriminant_value](discriminant-value.md)
 - [drop_types_in_const](drop-types-in-const.md)
 - [dropck_eyepatch](dropck-eyepatch.md)
 - [dropck_parametricity](dropck-parametricity.md)
+- [enumset](enumset.md)
+- [error_type_id](error-type-id.md)
+- [exact_size_is_empty](exact-size-is-empty.md)
 - [exclusive_range_pattern](exclusive-range-pattern.md)
-- [field_init_shorthand](field-init-shorthand.md)
+- [fd](fd.md)
+- [fd_read](fd-read.md)
+- [fixed_size_array](fixed-size-array.md)
+- [float_extras](float-extras.md)
+- [flt2dec](flt2dec.md)
+- [fmt_flags_align](fmt-flags-align.md)
+- [fmt_internals](fmt-internals.md)
+- [fn_traits](fn-traits.md)
+- [fnbox](fnbox.md)
 - [fundamental](fundamental.md)
+- [fused](fused.md)
+- [future_atomic_orderings](future-atomic-orderings.md)
 - [generic_param_attrs](generic-param-attrs.md)
+- [get_type_id](get-type-id.md)
+- [heap_api](heap-api.md)
+- [i128](i128.md)
 - [i128_type](i128-type.md)
+- [inclusive_range](inclusive-range.md)
 - [inclusive_range_syntax](inclusive-range-syntax.md)
+- [int_error_internals](int-error-internals.md)
+- [integer_atomics](integer-atomics.md)
+- [into_boxed_c_str](into-boxed-c-str.md)
+- [into_boxed_os_str](into-boxed-os-str.md)
+- [into_boxed_path](into-boxed-path.md)
 - [intrinsics](intrinsics.md)
+- [io](io.md)
+- [io_error_internals](io-error-internals.md)
+- [ip](ip.md)
+- [is_unique](is-unique.md)
+- [iter_rfind](iter-rfind.md)
 - [lang_items](lang-items.md)
+- [libstd_io_internals](libstd-io-internals.md)
+- [libstd_sys_internals](libstd-sys-internals.md)
+- [libstd_thread_internals](libstd-thread-internals.md)
 - [link_args](link-args.md)
 - [link_cfg](link-cfg.md)
 - [link_llvm_intrinsics](link-llvm-intrinsics.md)
 - [linkage](linkage.md)
+- [linked_list_extras](linked-list-extras.md)
 - [log_syntax](log-syntax.md)
+- [lookup_host](lookup-host.md)
 - [loop_break_value](loop-break-value.md)
 - [macro_reexport](macro-reexport.md)
 - [main](main.md)
+- [map_entry_recover_keys](map-entry-recover-keys.md)
+- [mpsc_select](mpsc-select.md)
+- [n16](n16.md)
 - [naked_functions](naked-functions.md)
 - [needs_allocator](needs-allocator.md)
 - [needs_panic_runtime](needs-panic-runtime.md)
 - [never_type](never-type.md)
+- [never_type_impls](never-type-impls.md)
 - [no_core](no-core.md)
 - [no_debug](no-debug.md)
 - [non_ascii_idents](non-ascii-idents.md)
+- [nonzero](nonzero.md)
 - [omit_gdb_pretty_printer_section](omit-gdb-pretty-printer-section.md)
 - [on_unimplemented](on-unimplemented.md)
+- [once_poison](once-poison.md)
+- [oom](oom.md)
 - [optin_builtin_traits](optin-builtin-traits.md)
+- [option_entry](option-entry.md)
+- [osstring_shrink_to_fit](osstring-shrink-to-fit.md)
+- [panic_abort](panic-abort.md)
 - [panic_runtime](panic-runtime.md)
+- [panic_unwind](panic-unwind.md)
+- [pattern](pattern.md)
+- [peek](peek.md)
+- [placement_in](placement-in.md)
 - [placement_in_syntax](placement-in-syntax.md)
+- [placement_new_protocol](placement-new-protocol.md)
 - [platform_intrinsics](platform-intrinsics.md)
 - [plugin](plugin.md)
 - [plugin_registrar](plugin-registrar.md)
 - [prelude_import](prelude-import.md)
+- [print](print.md)
 - [proc_macro](proc-macro.md)
+- [proc_macro_internals](proc-macro-internals.md)
+- [process_try_wait](process-try-wait.md)
+- [pub_restricted](pub-restricted.md)
+- [question_mark_carrier](question-mark-carrier.md)
 - [quote](quote.md)
+- [rand](rand.md)
+- [range_contains](range-contains.md)
+- [raw](raw.md)
+- [rc_would_unwrap](rc-would-unwrap.md)
 - [relaxed_adts](relaxed-adts.md)
 - [repr_simd](repr-simd.md)
+- [retain_hash_collection](retain-hash-collection.md)
+- [rt](rt.md)
 - [rustc_attrs](rustc-attrs.md)
 - [rustc_diagnostic_macros](rustc-diagnostic-macros.md)
+- [rustc_private](rustc-private.md)
+- [rustdoc](rustdoc.md)
 - [rvalue_static_promotion](rvalue-static-promotion.md)
 - [sanitizer_runtime](sanitizer-runtime.md)
+- [sanitizer_runtime_lib](sanitizer-runtime-lib.md)
+- [set_stdio](set-stdio.md)
+- [shared](shared.md)
 - [simd](simd.md)
 - [simd_ffi](simd-ffi.md)
+- [sip_hash_13](sip-hash-13.md)
+- [slice_concat_ext](slice-concat-ext.md)
+- [slice_get_slice](slice-get-slice.md)
 - [slice_patterns](slice-patterns.md)
+- [sort_internals](sort-internals.md)
 - [sort_unstable](sort-unstable.md)
 - [specialization](specialization.md)
 - [staged_api](staged-api.md)
 - [start](start.md)
 - [static_nobundle](static-nobundle.md)
-- [static_recursion](static-recursion.md)
+- [step_by](step-by.md)
+- [step_trait](step-trait.md)
 - [stmt_expr_attributes](stmt-expr-attributes.md)
+- [str_escape](str-escape.md)
+- [str_internals](str-internals.md)
 - [struct_field_attributes](struct-field-attributes.md)
 - [structural_match](structural-match.md)
 - [target_feature](target-feature.md)
 - [test](test.md)
+- [thread_id](thread-id.md)
 - [thread_local](thread-local.md)
+- [thread_local_internals](thread-local-internals.md)
+- [thread_local_state](thread-local-state.md)
 - [trace_macros](trace-macros.md)
+- [trusted_len](trusted-len.md)
+- [try_from](try-from.md)
 - [type_ascription](type-ascription.md)
 - [unboxed_closures](unboxed-closures.md)
+- [unicode](unicode.md)
+- [unique](unique.md)
+- [unsize](unsize.md)
 - [untagged_unions](untagged-unions.md)
 - [unwind_attributes](unwind-attributes.md)
+- [update_panic_count](update-panic-count.md)
 - [use_extern_macros](use-extern-macros.md)
+- [utf8_error_error_len](utf8-error-error-len.md)
+- [vec_remove_item](vec-remove-item.md)
+- [windows_c](windows-c.md)
+- [windows_handle](windows-handle.md)
+- [windows_net](windows-net.md)
+- [windows_stdio](windows-stdio.md)
 - [windows_subsystem](windows-subsystem.md)
+- [zero_one](zero-one.md)

src/doc/unstable-book/src/alloc.md

@@ -0,0 +1,7 @@
+# `alloc`
+
+The tracking issue for this feature is: [#27783]
+
+[#27783]: https://github.com/rust-lang/rust/issues/27783
+
+------------------------

src/doc/unstable-book/src/as-unsafe-cell.md

@@ -0,0 +1,7 @@
+# `as_unsafe_cell`
+
+The tracking issue for this feature is: [#27708]
+
+[#27708]: https://github.com/rust-lang/rust/issues/27708
+
+------------------------

src/doc/unstable-book/src/ascii-ctype.md

@@ -0,0 +1,5 @@
+# `ascii_ctype`
+
+The tracking issue for this feature is: [#39658]
+
+[#39658]: https://github.com/rust-lang/rust/issues/39658

src/doc/unstable-book/src/binary-heap-extras.md

@@ -0,0 +1,7 @@
+# `binary_heap_extras`
+
+The tracking issue for this feature is: [#28147]
+
+[#28147]: https://github.com/rust-lang/rust/issues/28147
+
+------------------------

src/doc/unstable-book/src/binary-heap-peek-mut-pop.md

@@ -0,0 +1,7 @@
+# `binary_heap_peek_mut_pop`
+
+The tracking issue for this feature is: [#38863]
+
+[#38863]: https://github.com/rust-lang/rust/issues/38863
+
+------------------------

src/doc/unstable-book/src/borrow-state.md

@@ -0,0 +1,7 @@
+# `borrow_state`
+
+The tracking issue for this feature is: [#27733]
+
+[#27733]: https://github.com/rust-lang/rust/issues/27733
+
+------------------------

src/doc/unstable-book/src/box-heap.md

@@ -0,0 +1,7 @@
+# `box_heap`
+
+The tracking issue for this feature is: [#27779]
+
+[#27779]: https://github.com/rust-lang/rust/issues/27779
+
+------------------------

src/doc/unstable-book/src/c-void-variant.md

@@ -0,0 +1,5 @@
+# `c_void_variant`
+
+This feature is internal to the Rust compiler and is not intended for general use.
+
+------------------------

src/doc/unstable-book/src/catch-expr.md

@@ -0,0 +1,7 @@
+# `catch_expr`
+
+The tracking issue for this feature is: [#31436]
+
+[#31436]: https://github.com/rust-lang/rust/issues/31436
+
+------------------------