Support for 'rsvp maybe' and some minor changes.
Support for 'rsvp maybe' and some minor changes.

1) added ability to respond to an event with 'rsvp maybe'. Maybe-rs
   are included in pings but have their own summary count. Pre-maybe
   events are automatically upgraded to maybe-friendly.
2) added Steven McCarthy & myself as collaborators (him for previous,
   me for this)
3) added 'rsvp status' as an (undocumented) synonym for
   'rsvp summary' because I just kept typing it over & over
   (probably because of 'git status')
4) fixed a bug that was inserting spurious copies of JSON data
   in weird places in the events.json file
5) removed some unneeded code:
   - an unused variable (lint insisted!)
   - duplicates of message strings which didn't need to be in rsvp.py
6) changed 'he' to 'they', because if even the BBC accepts a
   singular gender-neutral 'they', we can too :)
7) added some tests for maybe and for changing your response,
   and updated the 'yes' tests to expect a single space between 'is'
   and 'attending' instead of two spaces because I changed how the
   confirmation messages are generated

kokeshii/RSVPBot,recursecenter/RSVPBot,recursecenter/RSVPBot