Added authentication, TLS support and keyring support for SMTP

Also updated README (might conflict if previous pull request that renames README to .md extension has been merged). If so, fix is trivial or reject and I will rebase against upstream/master (thp:master).

The pull request is automatically updated. If you squash and force-push your changes (so they are one commit again), that'd make for nicer history, see here:

http://gitready.com/advanced/2009/02/10/squashing-commits-with-rebase.html