tls support

Hey Guys:

I needed TLS support so I could use log-iss to send logs to papertrail over an encrypted channel.  This actually did the trick!  Was kind of surprised how easy this was in the end.

Lemme know what you think. 
Then here you can say `if f.Set.Config.TlsConfig != nil` instead. Or if you feel that's too leaky you could make a UseTls() method that returns a bool that does the same thing to wrap it.