Implement HTTP webhooks as alternate method to mailing

[JayGoldberg]

email through raw SMTP is getting more difficult these days due to mail filtering, SMTP restrictions, and required SSL transports. Some embedded platforms don't have the mail command at all. Implement a way to invoke an HTTP GETs to a specified URL/IP using netcat or similar.

This would also have the nice side effect of revealing the IP that the RSTunnel host is at, in case that helps.