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`. 
One more—could you clarify where `send` comes from here, since without context it's not entirely clear that it's a `Service`? It looks like a method, and we don't want to send users digging for something they're not going to find.