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`. 
maybe this should be FINE or TRACE.  this seems like a lot to log at INFO, although maybe because it's email you expect it to be lower throughput?