Windows message handling into the Camera class
Fix missing null check in comptr
Expose various parts of the internal mesh loading process as methods on Mesh, so others can use them.
Add asserts to check for null arguments to various functions
Expand the texture API
- Add Texture2D, TextureCube, Texture3D classes
- Update load and create routines to use them
- Update the test app to use them
Release previous vertex/index buffers before uploading new ones to GPU