major refactoring render layer
add test interfaces
update unit test
Forgotten setting nullptr of mChildItem in SimpleLayer.
add RenderManager
add texture interface
update Canvas
update
Some Canvas comment fixes.
fix RenderBox
update demos
add VertexBuffer
change to std::exception
RotatingSkin prototype
RotatingSkin prototype (forgot to commit project)
major refactoring render system
RotatingSkin: custom center and fixes
major refactoring render system
RotatingSkin: custom center and fixes (forgot co commit header)