A TICKIT_BIND_ONESHOT flag, to make one-off event binds

A flag to make an event binding that removes itself after the first time it fires might be useful.

A little more efficient internally than simply removing itself also, if the binding needs the TICKIT_BIND_UNBIND flag, as having it remove itself will reïnvoke it a second time (recursively). A oneshot event would be invoked just once with both FIRE and UNBIND flags set.