Don't error about textures that aren't complete anyway
Optimise/improve hookset.pl, return dummy function pointers

* Now instead of returning NULL for entry points that we don't support and
  hoping the application will handle that or error out, instead we return
  a function that will log an error if it is ever called, and then pass
  through to the real function. In most cases, the capture will probably be
  broken as whichever function isn't saved.
* hookset.pl is much faster too, it outputs the whole gl_hookset_defs.h
  file and doesn't do multiple searches over the whole set of headers in
  official/ for each function.
Stop filtering wgl extensions, just return all we don't hook as-is

* I will assume for now that any wgl functions I don't explicitly hook have
  no effect on the captured frame and we can safely just let them straight
  through to the real function.
Make sure to return 'real' debug callback/param, not our own
Add EXT alias of glBlitFramebuffer for EXT_framebuffer_blit
Track and restore per-texture seamless cubemap state

* This is for the ARB_seamless_cubemap_per_texture extension. We already
  track the global state that isn't specific to a texture.
Handle ETC2/EAC in case, for GL_ARB_ES3_compatibility
Add some other aliases of functions we already implement
Update master list of GL extensions our code currently handles

* This list includes all extensions that we support all the entry points,
  tokens, etc for. It still needs to be unioned with the extensions that
  the implementation supports to determine what to return to the program.
* A couple of extensions are a little hazy as we implement everything in
  them that 'modern' GL includes, but the extension itself also specifies
  some old/outdated functions. Any extensions that are entirely old
  functions are omitted from this list.
Intersect renderdoc supported exts against driver supported exts

* For each context on first activation we fetch the extensions supported by
  the implementation, and intersect that with the list of extensions that
  renderdoc itself supports, so we return to the application the subset
  of 'real' supported extensions that we can support ourselves.
Fix a few typos, mostly using #define enum values not typed enum
Update to latest Khronos headers.
Implement EXT_polygon_offset_clamp
Implement GREMEDY string marker and frame terminator extensions

* We don't try and detect duplicate markers between GREMEDY and KHR_debug,
  just assume the program is smart enough to detect that both are available
  and pick only one to use.
Implement KHR advanced blend equation extensions
Add some more easily-implemented extensions
Add some EXT aliases and then report more supported EXT extensions
Add a list of extensions that I never plan to support.
Add a few more extensions we support, and some more we never will

* There are a handful of ARB and EXT extensions left that aren't in either
  the list of supported, or will-never support. These are ones that I want
  to support but haven't written the code for.
Add a note about vendor-specific extensions not being supported