Allow stylesheets to autocomplete hyphenated words

This is particularly handy for completing long variable names, such as those used in Bourbon.

Before:

![before](https://cloud.githubusercontent.com/assets/16124/3638916/cdc72546-1068-11e4-81d8-0f5e2db00c04.gif)

After:

![after](https://cloud.githubusercontent.com/assets/16124/3638917/d1803326-1068-11e4-91b8-1c07f60ab486.gif)