Add ActionBar-PullToRefresh 0.5. Fixes #10

Tested and working for me although I did have to add both lines to my build.gradle to make it work with ActionBarSherlock:

     compile "com.github.chrisbanes.actionbarpulltorefresh:library:0.5"
     compile "com.github.chrisbanes.actionbarpulltorefresh:extra-abs:0.5"

I thought I might just be able to use the second line and it would automatically bring in the dependency on the library but it didn't. Not sure if I've done something wrong. The gradle build files can be seen at: https://github.com/intrications/ActionBar-PullToRefresh/tree/gradle-build-for-mvn-repo