#107 Different boulder types

[Nodling]

There are two kinds of boulders in Haxima:
- the ones that are part of the map. They block movement, unless you're Mesmeme.
- the ones that Trolls throw at you. They don't block movement, and you can pick them up.

Things can get confusing when both boulder types are on the map. Two different boulder tiles would solve the problem.