Dependencies in gemspec declared, Gemfile.lock removed

It's recommended to not include the Gemfile.lock in a project, see
http://yehudakatz.com/2010/12/16/clarifying-the-roles-of-the-gemspec-and-gemfile/

Also, I declared the development dependencies in the gemspec and just
refer to that from the Gemfile.

Lastly, I declared two so far undeclared dependencies: thor & git
Removed rubyforge from gemspec
License specified in gemspec