Add conversion script of 1.3 to 1.4.

There is no data file format difference yet.
Sort resources in the quest tree by natural order. Fix #579.
Removed useless const qualifications for integer return types.
Removed redundant flush instructions.
Used std::atan2 to handle most of the work in get_distance.
Editor: fix opening an empty sprite. Fix #581.
Bugfix release 1.3.1.
Fix crash if an entity has a sprite without animation.
Remove unused fields.
Remove unused field (forgot to commit this file).
Fix sprite:on_animation_changed() called twice.

The event was called twice when changing the animation or direction of a
sprite.
Merge branch 'master' into cpp11

Conflicts:
	ChangeLog
	src/QuestProperties.cpp
	src/Sprite.cpp