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`. 
We don't need to describe what it doesn't do, describing what it does is sufficient.  However, for my edification, could you explain how you chose to just return a Future.Done?  Is the reply in the smtp spec anemic?