Added C-like API for GraphicsContext
Added C-like API for Texture
Added C-like API for vertex buffers
Added C-like API for D3DContext
Added C-like API for D3DTexture
Added C-like API for GfxLog
Use C-style constants in public API
Use opaque datatypes; Made C++ headers private
Removed typedef'ed enums; Cleaned up exports
General API cleanup
Merge branch 'capi'