Garbage collecting now reports ref cycles

Added logging to Squirrel garbage collecting.
Added "gc" command to console

It calls the garbage collector.
Added "performAction" method to Spawner base

This method is intended to be used to actually spawn the object(s) that
a spawner is responsible for.
Implemented "performAction" for ItemSpawner

ItemSpawner now will try to create an item and inject it into the world.
Whitespace fix
Added "currentRoom" property to GameWorld

The game world sometimes needs to pass around a room to be in,
especially when needing to create new game objects.
Moved item spawning logic out of GamePlay state

ItemSpawners now hold the logic to actually "spawn" an item, game states
just pass it a world and let it do its thing.
Fixed null-pointer issue

Since spawners can sometimes be null (because of my sub-par room parsing
routines) it's possible that you can have null spawners and then try to
iterate over them, calling methods and having an all-around bad time.
Merge pull request #49 from zackthehuman/master

Moved item spawning logic out of game play state, into ItemSpawner