Make all new types have UpperCamelCase names

Author: khandrym

src/types/alias.md

@@ -5,19 +5,15 @@ must have `UpperCamelCase` names, or the compiler will raise a warning. The
 exception to this rule are the primitive types: `usize`, `f32`, etc.
 
 ```rust,editable
-// `NanoSecond` is a new name for `u64`.
+// `NanoSecond`, `Inch`, and `U64` are new names for `u64`.
 type NanoSecond = u64;
 type Inch = u64;
-
-// Use an attribute to silence warning.
-#[allow(non_camel_case_types)]
-type u64_t = u64;
-// TODO ^ Try removing the attribute
+type U64 = u64;
 
 fn main() {
-    // `NanoSecond` = `Inch` = `u64_t` = `u64`.
-    let nanoseconds: NanoSecond = 5 as u64_t;
-    let inches: Inch = 2 as u64_t;
+    // `NanoSecond` = `Inch` = `U64` = `u64`.
+    let nanoseconds: NanoSecond = 5 as U64;
+    let inches: Inch = 2 as U64;
 
     // Note that type aliases *don't* provide any extra type safety, because
     // aliases are *not* new types