Migrated exiting non-source documentation to doxygen.  Migrated Universe.cpp to doxygen.  Reduced README and moved setup information to docs.
Added Audio docs
Added Input and related docs
Added Mesh*, Object*, and Raster to docs
Added Scene, Scissor, and Shader* to docs
Added Sprite, Texture, and Transform to the docs
Added more docs for Mesh*, Sprite, and Scissor
Fixed some improperly formatted lists in docs