Added changes to make the gem Rails 4 compatible

1) Updated gemspec to allow Rails 4.x
2) Made changes to specs and Rakefile to allow them to run under Rails 4
3) Modified specs to eliminate a number of deprecation warnings
4) Updated the Gemfile and database.yml so that the specs run against multiple Rails versions, JRuby
5) Added a .travis.yml
6) Added another AR class in specs to allow the specs to run against Rails 3.1.x