[GreenKeys] Slack client

[epvgk at limpoc.com]

Because I don't have enough ridiculous projects to do, I've written a teletype
client for the Slack messaging service which is pretty popular these days. On
the off chance anyone else here uses it, the client is at 
https://github.com/epvuc/loop-gateway/blob/master/slack_rtm.py
and is meant to work with the loop-gateway software 
https://github.com/epvuc/loop-gateway
though it really only needs "ser.py" which is the piece that interfaces with 
the hardware and exchanges data with client programs. I run it in a raspberry
pi zero.

eric