A main menu and enemy fixes

I have added a main menu and appropiate screens for credits and even an exit button! I have also fixed some enemy bugs and changed the behaviour of chests. They now stay open instead of being disappearing. Furthermore, if you die the main menu appears, instead of just preventing you from being able to move.

Happy adventuring,
DetoxSloth27 (jaker27)
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Known bugs:

• Enemies will push players beyond bounds
• Enemies do not drop loot yet
• Health counter doesn't show