Documentation nit.
Add painful tamer::distribute optimizations.

Bryan Kate observed that, if one collected a lot of at_trigger
or distribute events, you could blow out your stack. Don't do that.
Instead, when Tamer can detect that you are adding a new event
to a particularly simple distributed event, it'll just tack it
right on.

Signed-off-by: Eddie Kohler <ekohler@gmail.com>