Merge branch 'master' into develop
Add rules of traversability and sounds
Merge branch 'develop' of https://github.com/Renkineko/solarus-lstd into develop
Still debugging arrow

Now arrow works on crystal which activates blocks, but not as expected:
it uses the sprite collision detector instead of the touching. The
solid switches are not working for now but the bug may come from the
engine.
Merge remote-tracking branch 'renkineko/develop'