[OTFC][Daemon] Deletion of keys via http

Summary: Supports deletion of keys via http.

Test Plan:
Compile and start the server

  go build github.com/gow/otfc/daemon && ./daemon

Hit the daemon with the following requests

  $ curl  http://localhost:8088/delete?key=abc
  {"Status":"error","Err":{"ErrNo":2002,"ErrInfo":"key [abc]"}}

  $ curl  http://localhost:8088/set?key=123\&value="ssf   sfs"
  {"ErrNo":1004,"ErrInfo":"key [123]"}

  $ curl  http://localhost:8088/delete?key=123
  {"Status":"OK","Key":"123"}

Verify that no errors are returned.

Reviewers: tommy.testy

Reviewed By: tommy.testy

Differential Revision: http://dev.chetan.io/D40