cleanup and removal of json dependency

Hi,

A couple fixes and updates I figured might be welcome in the main repo:
1. Fixed the card test which was a bit out of date
2. Updated clj-http and clojure to the most recent stable releases
3. Simplified the request handlers to use the new clj-http syntax
4. Removed the data.json dependency as json parsing is now handled by cheshire built into clj-http

Let me know if you disagree with any of these changes. All tests pass with a valid token.