Special saves! (Resolves #162)

Closes #162

See merge request STJr/SRB2!1016

ACTUALLY fix #172

Closes #172

See merge request STJr/SRB2!1020

Delete connection screen and midgame joins

See merge request STJr/SRB2!1021

Increase the length of the player input buffer even more

See merge request STJr/SRB2!951

Expose "server" and "dedicated" to Lua scripts

See merge request STJr/SRB2!1022

Careful! Both are local variables and are always false for clients,
and therefore should obviously not be used in anything gamelogic-related.

It got removed by 864e7033 but he forget how it
was before the hook was there. :(

GameQuit Hook

See merge request STJr/SRB2!847

# Conflicts:
#	src/g_game.c

Faster OGL sprite sorting algorithm

See merge request STJr/SRB2!1008

Gametype fixes

See merge request STJr/SRB2!816

ACZ3 softlock fix

See merge request STJr/SRB2!1015

Don't repeatedly look for model texture files

See merge request STJr/SRB2!1009

Fix the Eggman signpost's background color

See merge request STJr/SRB2!1007

Faster and more correct OGL transparent surface sorting

See merge request STJr/SRB2!1005

GME cleanup and fixes

See merge request STJr/SRB2!1001

Fix missing bruh string in Lua side string options.

See merge request STJr/SRB2!1017

All this refactoring, just to resolve #162. Specifically, it engages savegame events not at level load (except for savefile start) but on level completion, just after you've gotten all the intermission bonuses but before the intermission actually starts.

Also fixes a never-before-discovered bug where if the titlemap has LF_SAVEGAME, your save file will be overwritten upon returning to the title screen. This game is a mess of hacks, I swear...

One unintended side effect: It may actually be faster in some speedrun circumstances in mods with cutscenes to complete the map, exit back to the title screen, and reload the file. It's a common feature of optimal runs in games with cutscenes, though, and Marathon Run has a toggle for cutscenes, so I'm not particularly bothered.

Backwards compatibility for shaderless hardware

See merge request STJr/SRB2!1003

MARATHON RUN

See merge request STJr/SRB2!941

OpenGL shaders

See merge request STJr/SRB2!724

# Conflicts:
#	src/hardware/r_opengl/r_opengl.c