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. 
Since you call osGetenv again inside the block, this would be more idomatic IMO.

`if pemFile := osGetenv("PEMFILE"); pemFile != "" {`

then use `pemFile` in instad on the next line.