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`. 
Yes, when testing with SMTP server stub and looking at its logs, I found out that this request is not actually sent from dispatcher, so I sought the way to enforce service(Request.Quit) before service.close(deadline).