`int` doesn't exist anymore. Usage of its equivalent `isize` is
discouraged since its size is platform-dependent. `i32` is used instead
in the examples. Also, integer suffixes aren't needed in the examples
anymore so we can just write `5` instead of `5i`.
This commit is an attempt to standardize the use of punctuation and
formatting in "The Rust Programming Language" as discussed in #19823.
- Convert bold text to italicized textcwhen referring to terminology.
- Convert single-quoted text to italicized or double-quoted text,
depending on context.
- Use double quotes only in the case of scare quotes or quotations.
