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`. 
Surprised to see email-headers are missing:
http://tools.ietf.org/html/rfc2076
http://kb.mediatemple.net/questions/892/Understanding+an+email+header

As a first step, it might be enough to offer headers as Seq[String]