Start allowing consecutive level save and load events (unfinished).
Add functions for protecting an mruby object from being GC’ed.
Fix typos
Fix minor issues with consecutive save events
Merge branch 'consecutive-save-and-load-events' into release-2.0.0
Fix incorrect type being passed to Get_from_Position()
Fix bonus box state not being saved.

This doesn’t fix the underlying problem; for some reason, the bonusboxes
are set off 1px when activated, making the save mechanism fail.
Add a climbing box to lvl_5