Metal Sonic Boss fixes

See merge request STJr/SRB2Internal!239

* Add more context clues to his fight, including an indicator for which laser attack is being used after chargeup.
* Make missiles able to vectorise him.
* Add another laser orb attack - vertical slice - and change the laser orb sequence to accurately reflect that horizontal is the hardest of the ones in 2.1.
* Optimise TC_BLINK, and fix an issue with TC_ALLWHITE that somehow avoided coming up in testing.
* Fix colorized bosses losing their colorization when flashing, by forcing TC_ALLWHITE.

* Remove PF_THOKKED every time a successful damage bounce occours.
* When this happens, spawn a number of particles based on thokitem at half scale! (Optimised, again, for MT_LHRT.)
* Also spawn these particles when a successful spring boost occours, as well as playing a twisted spring sound.

Also, some other related tweaks:

* Optimisations to A_VultureBlast, which was used as a base for the particle creation.
* Make the Metal Sonic boss use P_PlayerCanDamage instead of a custom, somewhat broken player damage detection mechanism.
* P_SpawnGhostMobj takes colorized into account.
* Fold Tails propeller damage into P_PlayerCanDamage.
* When performing an Attraction Blast, place the player in roll frames.
* Update all conditions preventing SH_PINK to incorporate thokitem and spinitem as well.
* Buff MT_LHRT travel distance at slow speeds.

# Conflicts:
#	src/p_mobj.c

Some small tweaks to level select

See merge request STJr/SRB2Internal!230

Startrings level header option

Closes #155

See merge request STJr/SRB2Internal!237

Boss fixes

See merge request STJr/SRB2Internal!235

HUD fixes

See merge request STJr/SRB2Internal!234

The amount of rings you start with also applies when you respawn from a starpost.

Startrings counts the ring total requirement for a perfect bonus.

Rain fixes and associated

See merge request STJr/SRB2Internal!233

Drawangle fixes

Closes #153

See merge request STJr/SRB2Internal!236

Prevent just anyone from skipping credits but allow admins

See merge request STJr/SRB2!478

Pk3 Leaks

See merge request STJr/SRB2!500

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

* Re-fix chat HUD position, and make it not move in match (which it needed to do in 2.1).
* Fix HU_drawPing for the new palette.
* Change the condition for greying out players, since the current one was buggy.
* Allow for tokens on the coop MP HUD, and use the small emeralds so there's space for them.
* Fix the mapping between skincolours and name colours in new chat, specifically to take into account every possible text colour (as opposed to the port previously done, which only used the 2.1 text colours and looked like ass as a result).

* Move HUD text's anchoring to underneath STR instead of above Lives.
* Adjust chat position slightly, to take advantage of SRB2's HUD layout having less content towards the bottom (unlike Kart, where it has roughly equal).
* Fix Match emeralds not displaying while in tab rankings with all-seven invuln/shoes bonus active.

* Like Kart, remove cv_precipdensity.
* Like Kart, replace "Infinite" draw distance value with "None".
* Better thinker with more return optimisation.
* Better placement of thinking in rendering, to avoid ceiling-mounted sprite glitches.

Add HUD icon for Pink shield. (Don't worry, this is my last expected commit in this branch. Gonna cherry pick everything unrelated to the Pink shield into a bunch of other branches now.)

ACZ hardcoding (including minecarts)

See merge request STJr/SRB2Internal!231