Adding dependencies

This is to help resolve issue #1

Right now dependencies aren't included in this gem. You can see on it's page over at rubygem's that no dependencies are listed: http://rubygems.org/gems/omniauth-goodreads

Right now you're using Jeweler which means you need to specify dependencies in the jeweler rake task. I added those in this commit. I also cleaned up the gemspec which listed jeweler as a dev dependency 4 times. I set this to create version 0.2.0 but if you want we can change that and you can release this as whatever you want.

IMHO: Jeweler is now overrated. Bundler has the ability to generate a gem skeleton, and editing the .gemspec file by hand is super easy. Easier than learning the jeweler abstractions. This pull request however just adds the dependencies, it doesn't do anything to remove jeweler.