Highlight code in `rustc --explain` (WIP)#39300

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estebank wants to merge 3 commits intorust-lang:masterfrom

estebank:code-highlight

Commits on Jan 22, 2017

Move code-highlight methods from rustdoc to own crate
estebank
committed

Commits on Jan 24, 2017

Add stdout syntax highlighter and highlight `--explain` code
estebank
committed

Commits on Jan 25, 2017

Simplify higlighting logic back while keeping term output
estebank
committed