Fix destination level not being saved in level exit.
Make menu_brown_1 playable
Add note to level reload in editor
Fix file-not-found exception when clicking “Reload” in the level editor.

It’s not useful to have the reload function re-execute the search
for the level file anyway, as the case that either the game level
file or the user level file suddenly disappears will never happen.
It will always be the very same file that gets loaded, so we can
safely skip the search process and just rely on the already existing
filename.

Also note that the reload function isn’t ideal. See the sourcecode
comments on this.
Remove all the global RClass* pointers
Move Load_Wrappers into cMRuby_Interpreter
Make `struct RClass*' pointers local.

As the mruby classes are linked inside the mrb_state object anyway,
there is no need to kep them at all. We can retrieve them at any
time using mrb_class_get().
Remove passing this to Init_ functions
Replace references to `struct RClass*' pointers with mrb_class_get().
Remove p_rc definitions
Fix mruby Path and Path::Segment
Fix Create_MRuby_Object() on some classes
Remove remaining references to global struct Rclass* pointers
Remove setup method from SMC module in mruby.

1. This wasn’t ever useful.
2. This is hard to implement with the non-global RClass pointers.
Fix classes being named a little different
Merge branch 'fix-multiple-mrubies' into devel. Closes #83.