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-Moved drawing code to a single function that takes linked list (should make it easier to optimize in the future).
-Implemented Z ordering of 2D nodes. Node2D and those that inherit have a visibility/Z property that affects drawing order (besides the tree order)
-Removed OpenGL ES 1.x support. Good riddance!
-Fixed many bugs in stretch mode
-Fixes to camera project and unproject as consequence of the above
-added setget to script (documented in script doc)
-more fixes to collada exporter for blender
