Fix MD2 rollangle in reverse gravity

See merge request !818

OGL horizon lines

See merge request !861

ExecCfg fixes

See merge request !821

Hide record & NiGHTS attack options if there are no available maps for them.

See merge request !868

Allow emblem hints (and radar) in record attack.

See merge request !820

Florida man fixes sectors with light level 256 blacking out OpenGL objects; mappers riot.

See merge request !840

Only initialise OpenGL if the user intends to load it (for real this time)

See merge request !796

Fix console backpic

See merge request !850

Turn FIXED_TO_FLOAT into a function

See merge request !869

Fix disconnected players being kicked for high ping

See merge request !866

use ATTRINLINE rather than inline to match some of the other functions in this file, though I'm told modern compilers ignore inlining info as they actually decide themselves now

(though I could pretend we still support the older ones lol)

Turn the fixed-float convert macros into inline functions, like those in GZDoom. The old macros get to be just the same as calling these inline functions.

Updates and fixes for the ZB config

See merge request !859

Skip empty gametypes in level select menu

See merge request !819

Remove the multi-file ZB configs. We're stick with the single-file config for ZB and doing all the UDMF stuff in UDB

NiGHTS Mode menu fixes

See merge request STJr/SRB2!841

Fix division-by-0 crash from 100% gamepad deadzones, and lack of input from 0% deadzones

See merge request !838

Actually use the "SCREENSHOT OPTIONS" header for its menu.

See merge request !832

Skins refactor

See merge request !843

Fix NiGHTS Attack crash after render mode change

See merge request !837

Fix HWR_DrawFlippedColumnInCache ignoring chroma key TF

See merge request !826

Replace NextTexAvail with glGenTextures

See merge request !828