Add in cocoapods support

I added a podspec! To use, drop the following into your Podfile:

target :test do
  pod 'Stubble', :git => 'https://github.com/SuperWes/stubble.git'
end

After the pull request you can change SuperWes to Stubble.

You might also want to add an email address to the spec.authors line.

Thanks guys!

-Wes