Highlight matches in search results

This adds highlighting matched text to the fuzzy search box and should address the issues described in https://github.com/atom/fuzzy-finder/issues/11.

I will be at the [Musical Desks](https://ti.to/github-events/musical-desks-2) event this week hacking on atom.io or my other [GitHub-related projects](http://philschatz.com).

Screenshot:
![image](https://cloud.githubusercontent.com/assets/253202/3085559/11675ca6-e514-11e3-8208-de7e141eef41.png)

Animated:
![fuzzy-highlights](https://cloud.githubusercontent.com/assets/253202/3085570/411e7e70-e514-11e3-9000-fd5952e43d39.gif)

**Note:** This adds `<strong>` around the matched characters but requires a change in CSS to show up white.