DX version now available

Since OpenGL drivers are famously buggy, I published DX version of the engine, there's still 1% missing though.

What's more, the issues in OpenGL version caused by AMD driver bug was fixed too.

I finally implemented multiple windows support which was necessary to fully make use of https://github.com/ocornut/imgui docking branch. You can see the result in action https://www.youtube.com/watch?v=ars8GYs7uE8