GSoC: finagle-smtp - initial

This is initial version of SMTP client for Finagle, which I am working on during GSoC'14.
For now it supports sending independent commands to SMTP server and sending a simple text email to one ore more addresses (without cc, bcc and reply-to). Usage is described in `README.md`. 
right--if you do `service(Quit) ensure service.close(deadline)` I think that will have the correct behavior, since it will wait for a response before tearing down the connection.  the two tcp connections will race to tear down, but I think that's OK.