Classes update + addition

- Enemy speed now is a value between 100 to 300
- add new Player 'key' attr
- add check for 'step on stone' to Player.update
- add Player.exits method
- add Exit.reset method
- edit Exit.render method so it deletes key when user steps on stone
- add 'level' variable
- move initialization of Enemies into its own function
Add checkProgress function

- check for players progress