Configurable Roles

I have added a new commit which incorporates some fixes from my last commit. I didn't intend for this to gain any type of attention (sorry for that) so I had some errors in the code that I committed that had to be fixed. I also updated the documentation to add the new option and describe the default behavior which is to perform tasks on the :app role. I also bumped the version number to 0.1.7. 

Thanks,
Jack