Write GA params to 1 cookie

* Write all Google Analytics Campaign params from url to one cookie with key of
ga_track rather than multiple cookies with the original param key as the cookie
key.
* Use JSON to seralize and unserialize the params hash when saving to and
reading from the ga_track cookie
Upgrade Jeweler Gem
Version bump to 0.3.0
Regenerate gemspec for version 0.3.0