Downgrade SDL2 to v2.28.5

See merge request !2369

compiling SRB2 with OSXCROSS for Mac Port

See merge request STJr/SRB2!2374

Do not fallback to Linux Makefile for Mac builds`
Do not build with libgme, it needs to linked with C++ runtime library

Apple was not including poll.h despite needing it.

These were not defined for macOS despite being necessary.

Delete old and unused rendering-related code

See merge request !2341

Fix various segfaults caused by missing P_MobjWasRemoved checks

See merge request !2052

Rendering cvars that control rendering walls, floors, and things.

See merge request !1526

Load TRNSLATE files from folders

Closes #1206

See merge request !2370

Fix credit sequence not compensating for non-green resolutions

Closes #1184

See merge request !2320

Fix insane TTY input latency

See merge request !2360

Change MAXSKINS from 256 to 255

See merge request !2365

Tokenizer mem

See merge request !2363

A value of -1 is sometimes reserved for "no skin", leaving 255 other values for skin numbers

Do not alllow error codepaths of UPnP to leave the mutex locked

Closes #1200

See merge request !2349

Issue #1150 - Fix it the right way!

See merge request !2350

This reverts merge request !2334

Merge remote-tracking branch 'origin/1200-next-cannot-load-game-when-using-srb2-launcher' into 1200-next-cannot-load-game-when-using-srb2-launcher

Fix tint equation shader

See merge request !2348

Print UPnP status to log file/external console only

See merge request !2347

Delete outdated docs

See merge request !2346

Add UDMF specification document

See merge request !2345

Cutscene timing fixed

See merge request !2344