Added Basic Enemy Chase and Obstacle Spawning

Player now chases an enemy. The enemy will spawn obstacles in the way to
try and slow down the player.
Spike Obstacle, if hit slows down player within a set number of frames,
if successfully avoided, the player gets a speed boost within a set
number of frames.

Block Obstacle, if hit slows down, no speed boost when avoided.

To do:
- more obstacles
- patterns for the obstacle spawning
- enemy attacks
- ending...when chase is finished or player cannot reach.
- minimap maybe?