Missed #ifdef HAVE_LIBGME in win_snd

See merge request STJr/SRB2!326

mixer_sound fix x64 build issue

See merge request STJr/SRB2!323

Save the current renderer to screenshots.

See merge request STJr/SRB2!324

Fix for object z positions on floating, bobbing FOFs

See merge request STJr/SRB2!316

Fix monitors (and other objects) on a floating, bobbing FOF being stuck slightly above said FOF after it has finished bobbing

OpenGL new clipping backport

See merge request STJr/SRB2!315

Alias recursion hotfix

See merge request STJr/SRB2!314

Compiling cleanup and fixes

See merge request STJr/SRB2!311

Made some efforts to improve efficiency of new code, hard to tell if I've made it better or worse though honestly

R_IsEmptyLine is now a thing too btw

More progress, NEWCLIP added to doomdef.h, sadly it actually all lags the game so I've disabled it for now

Other notes:
* on second thought I'll keep the hw_clip functions' gld prefixes rather than HWR, not like it matters either way
* despite the extra lag it does fix the issues with translucent walls and such when displayed at different vertical angles, such as with the GFZ1 waterfall

Other notes:
* Renamed all new functions to have HWR_ prefix instead of gld_, for consistency
* HWR_FrustrumSetup and HWR_SphereInFrustum are disabled and require HAVE_SPHEREFRUSTRUM. This is because 1) SRB2CB did not need the code, so presumably neither will we, and 2) there are some OpenGL API functions used there that due to our way of using OpenGL we don't use outside of r_opengl.c, which makes dealing with HWR_FrustrumSetup complicated in theory
* The new clipping functions are not added to OpenGL's "main" rendering code itself just yet, they're just available to use now once hw_clip.h is included

Opengl improvements backport

See merge request STJr/SRB2!304

Update readme

See merge request STJr/SRB2!313

Update copyright info

See merge request STJr/SRB2!309

Place limit on the amount of alias recursion allowed, to prevent cycles or otherwise excessive recursion

Minor remote viewpoint bugfixes.

Objectplace: Fix NiGHTS bumper angle being reset when WRITETHINGS

See merge request STJr/SRB2!299

Some code cleanup.

See merge request STJr/SRB2!298

yes I'm an idiot for rushing things like this

No hasslope

See merge request STJr/SRB2!312

"PlayerQuit" Lua Hook

See merge request STJr/SRB2!127