Merge branch 'hotfix/2.12.1'

* hotfix/2.12.1:
  * Tested against Ruby 2.1.3
Merge branch 'release/2.13.0'

* release/2.13.0:
  * Tested against Rails 3.2.20, 4.0.11 and 4.1.7 * Open-ended dependencies for development gems
  Improved readme [ci skip]
Merge branch 'release/2.14.0'

* release/2.14.0:
  * bootstrap 3.3.0
Merge branch 'release/2.15.0'

* release/2.15.0:
  * bootstrap 3.3.1
* Tested against Rails 3.2.21, 4.0.12 and 4.1.8
* Improved dependencies
* Improved readme
Merge branch 'hotfix/2.15.1' into develop

* hotfix/2.15.1:
  * Tested against Rails 3.2.21, 4.0.12 and 4.1.8 * Improved dependencies * Improved readme