Update LICENSE to 2013

Liked your note "It's 2012 already." Figured I'd push you along to 2013.
2013 is everywhere :calendar:
Update to released version of Rails 4
Rails4 :compact sass style is slightly different
Rails 4.0 is released, don't accept build failures anymore

[ci skip]
Move assets from vendor to app so the gem behaves more like a Rails Engine and the images are pre-compiled on Rails 4.
Merge pull request #54 from rafaelgaspar/develop

Move assets from vendor/assets to app/assets for Rails 4.0 compatibility
Restrict Rails 4 tests to Rails 4.0
Bump version to 2.3.2.1
Merge branch 'release/2.3.2.1' into develop

* release/2.3.2.1:
  Bump version to 2.3.2.1
Import Sass port of Twitter Bootstrap 3.0.0 (WIP)