Include version on bower.json

Bourbon’s version in Bower registry is still 3.1.8, which doesn’t include bower.json, thus installing files/paths that should be ignored.
Fixed deprecation warnings for sass-3.3-rc
Update to version 3.2.0.beta.2
Update sass dependency to => 3.3.0.rc.2
Update dist for bower
Merge pull request #312 from paulozoom/patch-1

Include version on bower.json
Updated bower to use correct tag version
More flexibility in button mixin

Issue #160