Setup Travis CI build matrix

## [WIP] Setup Travis CI build matrix

1) Setup a build matrix to allow Travis to test the following versions of ruby : 
   - 1.9.3
   - 2.0.0
   - 2.1.1

and the following versions of rails :
  - 3.0
  - 3.2
  - 4.0
  - 4.1

2) I took the opportunity to clean up the gem specifications file