Ratchicons pointing to wrong directory
We are getting broken links to the ratchicons font. I have checked this in Chrome, Safari, and Firefox on OSX, and AFAIK it would appear on other browsers and OS as well.
- Not sure if it matters, but we are using ratchet in a rails engine for our mobile site.
- The path to ratchet in the engine is `/vendor/assets/bower_components/ratchet`
- The fonts seem to be actually located at `/assets/ratchet/fonts/<font-name>`, but the css is pointing to `/assets/fonts/<font-name>`.

I think the simplest fix would be to make the directory for the fonts configurable, with a default of `../fonts`. 
This would mean changing:
https://github.com/twbs/ratchet/blob/d3e98c27c6f59072c330fd1897366a52f1103dd2/sass/ratchicons.scss#L9-L13
and: https://github.com/twbs/ratchet/blob/abc020333b1046d3e381c927b0e6a7a368bdf734/sass/variables.scss#L13

I'll submit a PR.
