We now only give users two options, to specify a stream and receive
public notifications for their goals, or to leave it out and receive
PMs and thus, keep their goals private. This simplifies the docs!
Rewritten in significant part by tabbott to actually be correct.
One particularly nasty thing the original webhook integration did is
do `current_time = time.time()` at the top of the `view.py` function
-- that means that code ran at import time, not runtime.