Percentage Width Support

I've taken @justindujardin's work from #407 and merged it with the most recent version of the ``master`` branch.

There are still some outstanding todos, but this is going to land in Chosen this week.

- [ ] Fix some issues in documentation that came from merging master
- [ ] Investigate whether or not we can support % width from style
- [ ] @mlharvest reviews CSS changes
- [ ] Click test