Update external links

[SaschaWillems]

There are several external links that no longer work or redirect to other pages. We need to check if we can point them elsewhere or if we just remove them because they're no longer of interest.

E.g.:

• http://www.amd.com/en-us/innovations/software-technologies/technologies-gaming/vulkan (Redirects to a page with no Vulkan refernences)
• https://www.phoronix.com/news/Apple-Silicon-Vulkan-MoltenVK (outdated information, better link to the MoltenVK repo)
• https://www.intel.com/content/www/us/en/developer/articles/news/new-intel-vulkan-beta-1540204404-graphics-driver-for-windows-78110-1540.html (links to an outdated driver)
• http://stackoverflow.com/questions/12524623/ (links to an SO post for OpenGL about color spaces, we should explain this in-place)
• http://glm.g-truc.net/ (Unsecure link that just redirects to the github repo, so we should use that instead)
• https://en.wikipedia.org/wiki/OpenGL_Shading_Language (Link to the GLSL spec instead)
• https://moltengl.com/ (Should point to the MoltenVK repo instead)

[SaschaWillems]

Wen't through all the links and updated where it applies.