Some preliminary work to make multiple bosses in the same map work nicely together, by allowing parameter to alter the linedef executor tag to call in increments of 100.

Also: Making sure every single reserved tag is recorded as an LE_ constant.

As I wanted MI to do but he was too exhausted at the time from hardcoding, make the Fang bullet knockback less hardcoded and instead give it MF2_SUPERFIRE.

# Conflicts:
#	src/p_mobj.c

ACZ hardcoding (including minecarts)

See merge request STJr/SRB2Internal!231

Stand(alone) lump comedy

See merge request !499

FOF slopes level load fix

See merge request !498

libopenmpt support

See merge request STJr/SRB2Internal!229

Fix warnings/errors found during compiling, mostly of the mixed-declaration-and-code or shadowed variables variety

Part 2 of fix, make sure copied slopes also pass on hasslope status to attached target sectors for FOFs

Also fix whitespace to use tab-style spaces instead of regular spaces, ew

Fix FOF slopes briefly glitching on level load in software mode, by ensuring the FOFs' target sectors have hasslope set on creation

(Hopefully) fixed the player sometimes landing on the solid part of the minecart stopper after being launched out of the minecart

Portal-based skybox rendering replacement for the software renderer

See merge request STJr/SRB2Internal!226