Improvements to `BTreeSet` documentation.#38208

Merged

bors merged 4 commits intorust-lang:masterfrom

frewsxcv:btreesetdocs

Dec 21, 2016

Commits on Dec 14, 2016

Indicate `BTreeSet` in docs is code-like.
frewsxcv
committed

Commits on Dec 15, 2016

Commits on Dec 20, 2016

Indicate that `BTreeSet::iter` returns values in ascending order.
frewsxcv
committed