Improved some code and added README and TODO

I've improved the code in platformer.py (in python spaces are used instead of taps to make indent)
I also added a README and a TODO file to improve the social experience (sounds weird lol)
I made some changes to actually kill the player instead of only rising the health bar beyond zero, I also made some changes so only the enemy with made contact with the player hurts him and not **all** the enemies like before.