Added opacity modifier and fixed arrow key commands for reverse scroll direction.
Refactored opacity modifier.
Merge pull request #16 from tmoc/opacity

Created and refactored opacity modifier.
Fixed bug where crossing over the end of position too fast put the position in the wrong place.
Merge pull request #17 from onetruebob/fixModifierStarts

Fix modifier starts
Actor factory now able to create image surfaces on actors.