Changes to make sdl-opengl-minimal a better starting point for user's own programs

[euccastro]

The most critical one is probably the one that initializes GLEW at the right point to avoid segfaults when you use some OpenGL functions. Others are more cosmetic but worth including, I think.

[alvatar]

Thanks Estevo, glewInit should be wrapped in a cond-expand for desktop/mobile paths. That function will break mobile version. I find it cleaner to handle events in a COND, as done in the other templates, but that's ok.

[euccastro]

Yeah, I agree cond is better; I'll change that and resubmit.

And yes, I'm only testing on desktop so far. I'll try and add a cond-expand as you say, by looking at how it's done elsewhere, but I have no means to test that ATM, so please verify before you merge.

[euccastro]

OK, fixed both I think. I just borrowed the cond-expand from the sdl-opengl generator, so it should be fine.

[alvatar]

Great! Thanks :)