Hide NiGHTS grade in singleplayer if ranking is below GRADE_A

Closes #250

See merge request STJr/SRB2Internal!377

(Resolves #250)

Make ACZ3 Boss damage while bouncing more lenient

See merge request STJr/SRB2Internal!375

Add scroll-wheel weapon changing to default controls

Closes #248

See merge request STJr/SRB2Internal!374

Fix bogus "requested skin not found!" print

Closes #247

See merge request STJr/SRB2Internal!373

Fix for A_ConnectToGround on gravflipped objects

See merge request STJr/SRB2Internal!372

Kart-port bugfixes (round 1)

See merge request STJr/SRB2Internal!371

Fix condition which was MEANT to allow attacking Fangboss from the side while bouncing, but instead made it extremely difficult to pull off.

(resolves #248)

Also, since I'm less paranoid now - readd the skin number to its print.

On the recommendation of Sryder, revert everything relating to the `cpusleep` changes except for the new default value of 1.

Mixed declaration + out-of-bounds GCC error fixes for OpenMPT fixes (can't believe I didn't catch the former earlier)

* Default to 1, which means potential for a 1-frame loss every once in a while but no longer a complete cpu hog
* New minimum is 0, since -1 just did the exact same thing as 0 except slightly more optimized.

OpenGL sky dome

See merge request STJr/SRB2Internal!350

libopenmpt related changes

See merge request STJr/SRB2Internal!351

Reduce speed sneaker factor to 1.67x

See merge request STJr/SRB2Internal!368

Correct minor OGL regressions

See merge request STJr/SRB2Internal!361

Left and Right Arrow keys also select level in Record Attack

See merge request STJr/SRB2Internal!363

Amy tweaks

See merge request STJr/SRB2Internal!366

RVZ hardcode

Closes #178

See merge request STJr/SRB2Internal!357

Amy for Frozen Hillside (full pitch in description)

See merge request STJr/SRB2Internal!356

Only apply NiGHTS draw distance to hoops

See merge request STJr/SRB2Internal!370

Increased THZ goop speed by 25%

Closes #229

See merge request STJr/SRB2Internal!367

Only apply NiGHTS draw distance to hoops, because it turns out they're pretty much the sole cause of NiGHTS lag

# Conflicts:
#	src/p_map.c

Fix the sky on the intro cutscene not scrolling.

Closes #220

See merge request STJr/SRB2Internal!353

Headbumps and associated

Closes #242

See merge request STJr/SRB2Internal!360

Change the time NiGHTS bumpers aren't responded to to 5 tics rather than 9.

Closes #246

See merge request STJr/SRB2Internal!365

ACZ touchups

Closes #209, #208, and #158

See merge request STJr/SRB2Internal!359

Don't deplete special stage timer in water if you have water protection

See merge request STJr/SRB2Internal!364