[#3] Initial REST API

- Added a proper processable workflow with a custom
  validator function and dispatching based on media type.
- Removed ring json in favour of later decoding that
  fits better with the liberator processable callbacks.
- Added generic not found strategy.
- Swaped media type supprot from clojure to edn.
- Added inital simple tests.
- Changed fixture data structure to match a
  typical db record.
- Added logic for not found in resources.
- Updated README to highlight that it's WIP.