Added all derelict2 WGL Extension

Instead of generating the import code with some external tool, I used what is already available in D: mixins.
It will be easier to change the code from now on and I think all the other modules should use a similar approach.

Edit:
Fixed loadGLFunc and changed the name of the `winext` module .
I noticed derelict use `static if(Derelict_OS_Windows)` instead `version(Windows)` so I didn't touch that.