Added support for 2D shadow casters.
*DANGER* Shaders in CanvasItem CHANGED, if you are using shader in a
CanvasItem and pull this, you will lose them. Shaders now work through a
2D material system similar to 3D. If you don't want to lose the 2D
shader code, save the shader as a .shd, then create a material in
CanvasItem and re-assign the shader.
-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
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-Fixed small bugs all around
-Added ability to show/hide entire sections of the spatial (3D) tree
-WIP new vehicle (not ready yet) based on Bullet
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-Begin work on Navigation Meshes (simple pathfinding for now, will improve soon)
-More doc on theme overriding
-Upgraded OpenSSL to version without bugs
-Misc bugfixes
