Pickups now have collection delay when vomited

Implements FS#394.
Merge pull request #286 from tigerw/pickupdelay

Pickups now have collection delay when vomited
Unified cPlayer's Heal() function with cEntity's.
Cleanup in cPlayer.
APIDump: Documented cItemGrid and cPlayer.
Fixed cPickup's constructor's parameter naming.
APIDump: Documented cPickup.
APIDump: Documented cEnchantments.

The constants are self-documenting, no need to describe them further.
cPickup cleanup.
Renamed cMonster::GetSpawnRate() to GetSpawnDelay().
APIDump: Documented cMonster.