secondary game state added, it provides a way of displaying messages (and potentially other graphics or text) on top of the any game state(s) without having to interrupt them.
Minor downside: some parts of the code still run when they shouldn't, e.g. mouse clicks are still registered by the active game mode.
previously mentioned mouse issue fixed
Merge branch 'develop' into feature/issue/#63

Conflicts:
	love2d/data/map/tutorial1.ini
	love2d/main.lua