Independent axes for sprite-sprite collisions

[robbrit]

Right now when sprites collide at all, it halts the movement. This isn't ideal, it'd be better to be able to "slide" - if you are moving diagonally and hit another sprite, you should slide along the sprite in the direction that the sprite isn't in.

For example if you're moving down and right and you bump into a sprite on your right, you should continue sliding down.

This might be a bit tricky because sprites can also move. We'll probably want to apply the X and Y moves separately:

for each sprite:
  move it in the X direction
  check for collisions with walls
  check for collisions with other sprites

revert X for any that hit things
repeat for Y