Add a simple example of modern OpenGL (3.3) with shaders. 

It took me quite a lot of frustration and messing around to get a basic example of GLFW3 with modern OpenGL (3.3) with shaders etc. working.

I thought adding what I figured out as an example might save somebody else some time and frustration. It's pretty simple, but getting the window hints and gl.BufferData right for example was not at all obvious (for me).