New jumping improvements

Just to improve the game, I learned to implement the "Coyote time", now there is a 0.1 second of chance to jump when leaving a platform. Also, I implemented a "Buffered jump" so you can immediately jump if you pressed jump just a0.1 seconds before jumping. Last, I made so that to jump at max height you have to maintain the jump button pressed, the moment is released, the character will stop the jump and start falling.

The game is quite sort it may not need these changes, but I wanted to implement these jump properties that are usually available in platform games.