cleanup: remove superfluous assignment of .tile property

the .tile property should already have the right value when this
method is entered
cleanup: better to use 'tile' than 'rawTile' in TerrainBehavior
api: setTile() no longer accepts upper bits

also- eliminate "rawTile" from TileBehavior class and subclasses
MakeTiles: refactor: pushing caching down a level
MakeTiles: refactor: load images at parse time

this will allow me to detect and load animations (in a future commit)
MakeTiles: use constant (STD_SIZE) to represent standard tile size of 16px