Add HTTPS Support

This may fix https://github.com/mthenw/frontail/issues/15, I needed a way to start an HTTPS server so I simply added a way to pass in a path to a key.pem and a cert.pem file, if these are passed in, it will start an HTTPS server, otherwise it'll continue with an HTTP server.

I threw this together pretty quick, so feel free to modify as you see fit.

Thanks,

Andrew Davis
NASA - Kennedy Space Center