Memcache Plugin: Support memcached protocol

[kimchy]

Allow to use memcached protocol to interact with elasticsearch. Basically, the idea is to expose elasticsearch REST interface over memcached protocol. In general, the key part of the protocol is the REST uri used. For set command, the body is the REST body (http body). For get commands, the return payload is the body. set translates to POST, get translates to GET, and delete translates to DELETE. Note, this are the only commands implemented (and quit).

Note, memcached imposes restrictions compared to the REST protocol. set can not return a body for the response, and get can't accept body for the request (note, the uri can have query parameters).

[kimchy]

implemented.