Document inclusive ranges.

[alercah]

This provides documentation for rust-lang/rust#28237.

[alercah]

Note that the failing build is due to using an un-stabilized feature; it should pass once the feature is stabilized and released.

[steveklabnik]

These just landed as stable in nightly. Let's retry travis!

[alercah]

Looks like it's failing; is it running stable and/or not up to date with the nightly?

[marioidival]

@alercah Rust stable https://github.com/rust-lang/rust-by-example/blob/master/.travis.yml#L5

[frewsxcv]

seems like we'll need to do one of three:

• wait until it lands in stable rust, then merge
• ...or update travis to use nightly rust
• ...or update the code block to be rust,ignore

@steveklabnik thoughts?

[frewsxcv]

actually, since rust-by-example now rides the docs release train, seems like it should be safe to do the second option and turn on nightly rust for travis ci

[steveklabnik]

Yes, that's what we should do. Run with nightly but check there aren't any feature gates.

@alercah are you interested in tackling that? If not, I can take care of it tomorrow :)

[frewsxcv]

looks good, thanks!