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`. 
there's a ton of duplicated code here, which doesn't seem strictly necessary.  let's also unalign this, we don't use that style elsewhere in finagle.