Rollup merge of #39944 - GuillaumeGomez:associated-consts, r=frewsxcv

Improve associated constant rendering in rustdoc

Before:

<img width="1440" alt="screen shot 2017-02-19 at 00 30 51" src="https://cloud.githubusercontent.com/assets/3050060/23097697/caeed80e-f63a-11e6-98c2-5d27e4efd76d.png">

After:

<img width="1440" alt="screen shot 2017-02-19 at 00 30 39" src="https://cloud.githubusercontent.com/assets/3050060/23097698/cfb4874e-f63a-11e6-80cf-ffbf5c5c6162.png">

cc @SergioBenitez

r? @rust-lang/docs

diff --cc src/librustdoc/clean/mod.rs
Simple merge

diff --cc src/librustdoc/html/highlight.rs
Simple merge

diff --cc src/librustdoc/html/render.rs
Simple merge