Fix links on keyword docs.

- Make links relative.
- Adjust links from old 2018-edition book.
- Fix broken link in `let` docs.

Fix links on keyword docs.

- Make links relative.
- Adjust links from old 2018-edition book.
- Fix broken link in `let` docs.

Fix links on keyword docs.

- Make links relative.
- Adjust links from old 2018-edition book.
- Fix broken link in `let` docs.

Rollup of 18 pull requests

Successful merges:

 - rust-lang#59612 (Use normal newtype_index macro for MIR dataflows)
 - rust-lang#59675 (Stabilize the `alloc` crate.)
 - rust-lang#59708 (Mark variables captured by reference as mutable correctly)
 - rust-lang#59735 (remove lookup_char_pos_adj)
 - rust-lang#59747 (Copy book.toml unstable book generator)
 - rust-lang#59796 (Retire `IsNotConst` naming)
 - rust-lang#59804 (Clean up jobserver integration)
 - rust-lang#59818 (Eliminate `FnBox` usages from libstd.)
 - rust-lang#59830 (Fix links on keyword docs.)
 - rust-lang#59835 (Re-export NonZero signed variant in std)
 - rust-lang#59852 (std: Add `{read,write}_vectored` for more types)
 - rust-lang#59855 (Fix attributes position in type declaration)
 - rust-lang#59858 (Make duplicate matcher bindings a hard error)
 - rust-lang#59879 (Use SecRandomCopyBytes instead of /dev/urandom on MacOS)
 - rust-lang#59899 (In `-Zprint-type-size` output, sort enum variants by size.)
 - rust-lang#59912 (MaybeUninit: remove deprecated functions)
 - rust-lang#59925 (Fix paste error in split_ascii_whitespace docs.)
 - rust-lang#59930 (Exclude some copies of old book editions from search engines)

Failed merges:

r? @ghost

Rollup of 18 pull requests

Successful merges:

 - #59612 (Use normal newtype_index macro for MIR dataflows)
 - #59675 (Stabilize the `alloc` crate.)
 - #59708 (Mark variables captured by reference as mutable correctly)
 - #59735 (remove lookup_char_pos_adj)
 - #59747 (Copy book.toml unstable book generator)
 - #59796 (Retire `IsNotConst` naming)
 - #59804 (Clean up jobserver integration)
 - #59818 (Eliminate `FnBox` usages from libstd.)
 - #59830 (Fix links on keyword docs.)
 - #59835 (Re-export NonZero signed variant in std)
 - #59852 (std: Add `{read,write}_vectored` for more types)
 - #59855 (Fix attributes position in type declaration)
 - #59858 (Make duplicate matcher bindings a hard error)
 - #59879 (Use SecRandomCopyBytes instead of /dev/urandom on MacOS)
 - #59899 (In `-Zprint-type-size` output, sort enum variants by size.)
 - #59912 (MaybeUninit: remove deprecated functions)
 - #59925 (Fix paste error in split_ascii_whitespace docs.)
 - #59930 (Exclude some copies of old book editions from search engines)

Failed merges:

r? @ghost

Fix links on keyword docs.

- Make links relative.
- Adjust links from old 2018-edition book.
- Fix broken link in `let` docs.

Fix links on keyword docs.

- Make links relative.
- Adjust links from old 2018-edition book.
- Fix broken link in `let` docs.

Rollup of 16 pull requests

Successful merges:

 - #59675 (Stabilize the `alloc` crate.)
 - #59708 (Mark variables captured by reference as mutable correctly)
 - #59735 (remove lookup_char_pos_adj)
 - #59747 (Copy book.toml unstable book generator)
 - #59796 (Retire `IsNotConst` naming)
 - #59804 (Clean up jobserver integration)
 - #59818 (Eliminate `FnBox` usages from libstd.)
 - #59830 (Fix links on keyword docs.)
 - #59835 (Re-export NonZero signed variant in std)
 - #59852 (std: Add `{read,write}_vectored` for more types)
 - #59855 (Fix attributes position in type declaration)
 - #59858 (Make duplicate matcher bindings a hard error)
 - #59899 (In `-Zprint-type-size` output, sort enum variants by size.)
 - #59912 (MaybeUninit: remove deprecated functions)
 - #59925 (Fix paste error in split_ascii_whitespace docs.)
 - #59930 (Exclude some copies of old book editions from search engines)

Failed merges:

r? @ghost