Add ability to choice between EGL and GLX on linux, without changing the opengl version.

[goddessfreya]

No description provided.

[sumit0190]

@zegentzy Are you working on this already? I started using this in a project a couple of days ago and I thought "this'd be a nice-to-have" and started hacking on it, but only later realized that this was made into an issue already.

[goddessfreya]

If you already have it done against master, I'd be happy to merge it in for v0.22.

I'm only working on having this ready for v0.23, via the upcoming plat_attrs in ContextBuilder.

[sumit0190]

Oh I'd have to clean it up by loads: what I have right now is a terrible hack I put in just to test my logic with both EGL and GLX.
I see that PlatformAttributes isn't in yet; maybe we should take this up AFTER you push your changes in?

[goddessfreya]

Well yeah, cause like I said, I only intend to have it in for v0.23. If you want it in v0.22, you can backport the neccecary changes and put up a PR.

[sumit0190]

Sure thing, I'll wait; until then I'll look at other issues I can contribute to. Thanks!

[goddessfreya]

Implemented in v0.24. See #1271. Closing.