Update documentation to OpenGL 4.6

[NogginBops]

Fixes #72

[NogginBops]

Afaik this PR should be ready with at least the most impactful 4.6 changes.

@oddhack is there any possibility of getting this or any of the other PRs merged?
#149 #148 #147 #145 #144
#143 #142 #141 #140
(and if these can be merged I can also finish #146 so that they all can get merged)

[eloj]

I just watched someone get confused on stream, because they were recommended glMultiDrawArraysIndirectCount, but it isn't documented at https://registry.khronos.org/OpenGL-Refpages/gl4/ because this repo is stuck at gl4.5

I don't normally ping people, @oddhack, but is there a reason not to merge this and the rest of the MRs above?

[manpat]

thank you for merging this!