Fix weather-dependent healing moves.

These aren't done with a rounded fraction like the other healing moves. They heal the target by an amount equal to it's maxHP modified by either 0xAAC (.667), 0x800 (0.5), or 0x400 (0.25)
Proprly implement Swallow's healing as well
Move healing to onHit from onModifyMove
Merge pull request #287 from V4Victini/patch-8

Fix weather-dependent healing moves.