Formatting chapter: Add example about Show

[japaric]

Rebased #129, dealt with style nits, renamed chapter/section and reworded introduction.

@vojtechkral Could you review the changes? Also, you may want to look at the work plan for the formatting chapter.

[vojtechkral]

Looks great.

I think it should be mentioned at some point that to format for {:s} one needs to implement str::Str rather than fmt::String, otherwise the reader might be surprised by a compiler error...

[japaric]

Looks great.

Ok, then I'll merge this.

I think it should be mentioned at some point that to format for {:s} one needs to implement str::Str rather than fmt::String, otherwise the reader might be surprised by a compiler error...

I think that's actually a bug that occurs when you have a generic impl (impl<T: Str> Foo for T) and you try to add a second impl that doesn't overlap (impl Foo for int).

That bug should (hopefully) get solved by the trait reform that's coming at some point. But, yes, we can drop a note about in somewhere in the chapter.

[japaric]

@vojtechkral Thanks for the initial PR and the review

[vojtechkral]

That bug should (hopefully) get solved by the trait reform that's coming at some point. But, yes, we can drop a note about in somewhere in the chapter.

Ok, that's good to hear, in that case the note about Str is probably not needed that much...