multiplayer basics

Demo:
-resource loading now handled on construction

Multiplayer:
-added difficulty as a constructor parameter
-removed sizing bug caused by calculating based off the window BEFORE it
was resized
+moved most contruction logic into start()
-update now passed on to game instances
-input events now passed on to game instances
-will close when Escape is pressed
!probably doesn't want to be that easy once an actual game is running