Added DELETE debug endpoint

References #100

Added support to respond to HTTP DELETE request to debug endpoint.
Documented error responses currently returned. There will be some
additional error responses once we've determined the exact response from
the underlying abstraction layer. Probably a 404 message for when the
origin/hash pairing does not match to the database.

Also, the delete endpoint should probably refactor to return a 204
status code on success. See the relevant stack overflow post:
http://stackoverflow.com/a/6440374/1808164