Fix handling of winning stats

Previously any stat in a game would prevent future stats in that
game taking affect, per user.

(e.g. a scrub stat followed by a win would ignore the win, even if
no prior wins were counted)

We now only block subsequent win stats, rather than any stat by the same
user.

Fix custom user padding

This was never seen before as we were shortening the padding rather
than lengthening, and changed user names hadn't been long enough
to show the bug.

Update README

Remove cancelled games from the stats

Restructure stats ordering - base on win ratio

Fix off-by-one in game ending overlap check

send_message() returns early for no text

Don't say anything if a non-participant removes a 👍

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