- Various warning fixes for MSVC warning level 4 with warnings as errors.
- Implemented OpenGL support using glQueryCounter. This may not work on MacOS X which is a bit behind on its OpenGL support, but it was much simpler to implement -- glQueryCounter gives us a timestamp in ns, whereas GL_TIME_ELAPSED queries (which MacOS X supports) give an elapsed time only so it's more work to get accurate start, end values.
- Updated the readme to show the addition of support for OpenGL, though since it's a copy-paste of the D3D11 section you may just want to remove the OpenGL section and say it's almost the same for OpenGL (only the Bind function changes, it doesn't take any parameters).