bugs in shade

This is a terrible system but will suffice for the time being.

Bugs

Grid is currently a “loose” grid should change to become a “strict” grid; this leads to bugs:
- Ray casting sometimes doesn’t work and a mole will end up going for something it shouldn’t “see”.
- The mushroom placing algorithm is not correct. It sometimes places mushrooms too close to or even inside an obstacle.
Movable objects, it currently matters the order in which you call repel, it shouldn’t matter. (May be fixed by strict grid.)