Remove local-only build files from source control.

In the case of CocoaPods, each user should maintain their own copy of
the required depenencies using `pod install` and `pod update`.
Remove JSONKit as a dependency.

It is unused, and because we've specified iOS 6 as our base SDK
version, we can reliably use NSJSONSerialization everywhere.
Merge pull request #2 from jparise/remove-jsonkit

Remove JSONKit as a dependency.
Merge pull request #1 from jparise/gitignore

Remove local-only build files from source control.