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`. 
I'm not sure this is the right layer to have this at.  Maybe it would make more sense in your dispatcher?  Then you wouldn't entail a new allocation every time you requested a new connection.