This includes a new example with Rectangle, instead of reusing HasArea,
because fn area would require the Mul trait, and the added complexity of
that would be better left for the Operators and Overloading chapter.
Squashed at reviewer's request: Move teaser for trait bounds to bottom
This adds strictly more information to the source files and reduces the
need for customized tooling to render the book.
(While this should not change the output of _rustbook_, it is very
useful when rendering the sources with external tools like Pandoc.)
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.
