Plans for making a maze

This commit contains steps 1 - 3

1. Load an image with maze walls a certain colour.

2. create a 2-dimensional array that fills the screen (with gridsize
spacing)

3. In setup(), scan through each value in the array and check the colour
of each pixel. If pixel is wall colour, boolean = false, else = true

4. create booleans in Pac class for up, down, left, right. Set these to
false.

5. in Pac.move(), run a check to see whether, in the direction of
movement, Pac is going to hit a wall (boolean = false)