Fixed a few typos in extension names, fixed BPTC texture compression
typos. Removed redundant EXT_framebuffer_object from functions as the
Framebuffer class itself has it.
It's slight copypaste, because operator| doesn't accept typedefs and
extracting the algorithm from Renderbuffer would cause the code to be
overcomplicated and not prepared for more buffer texture/renderbuffer
format additions.
The requirements are cross-referenced to dedicated page, similarly to
TODO and bug lists.
Also updated / improved documentation for some texture / image formats.