"prefoppositecolor" - exists solely for metal so he can have his sonic 4 peridot-background end sign when using skincolor_blue. not updating player.dta yet though.

Let's be consistent with how other parts of the code handle this same issue of conditional operations surrounding non-conditional operations.

Fixing a bug which could be caused by tapping up/down on the character select at high speeds by ensuring that o is never negative instead of assuming the one circumstance it may have been negative under.

* When moving slowly, P_InstaThrust at S_SKIN's maxdash forward, and set momz to S_SKIN's mindash upwards. Plays a tok noise (not thok). Hurts enemies/bosses, busts spikes/monitors/all types of bustable blocks.
* When moving quickly... doesn't do anything yet, but WILL do a slide.

Also, P_DoSpinDash is now renamed to P_DoSpinAbility, and CA_TWINSPIN users can bust all bustable blocks on collision too.

* CA_TWINSPIN - you can do it multiple times
* CA_DOUBLEJUMP - your jump height is reduced each time, like in Kirby games. The number of extra jumps once you've left the ground that are available is determined by the character's actionspd.

Dashmode users can break spinbust blocks when dashing, twinspin users can break both spinbust and Knuckles-only blocks when twinspinning.

Also, the gravity of drowning characters has been reduced to look more natural.

Merge branch 's_skinprovements' of http://git.magicalgirl.moe/STJr/SRB2Internal.git into s_skinprovements

* Electric sparks coming off entire body instead of bubbles coming out mouth
* Different sounds.
* Different icons.

These sprites are currently local only, but I'll be doing a lot of asset updating this evening since Rob asked me to so it won't be long until you can get them.

Revert of the FF_MIDDLESTARTCHANCE changes for player states, although the flag still exists internally since there's no reason to remove it.

# Conflicts:
#	src/d_player.h
#	src/dehacked.c
#	src/info.c
#	src/p_user.c

Sideways springs, horizontal hog-launchers, perpendicular plungers...

Call them what you like, they're in the code now. And have been for months!

Nev3r uses the hell out of these and I'm fed up of them being <!>'s all over the place, so please have 'em in master so we can update srb2.srb and make things better for all of us.

See merge request !30

Cleanup of P_CheckUnderwaterAndSpaceTimer's conditional checks for future PF_ROBOT changes, where characters like Metal make electric zaps instead of bubbles.

Dashmode

This branch Metal Sonic's abilities (CA_DASHMODE) to the game.

See merge request !26

Ported CA_HAMMER from new-character-actions in a way that takes advantage of all of the non-hardcodey things I've added in this branch.

Also, it's called CA_TWINSPIN because that's more inoccouous.

On MI's reccomendation, a skin flag to disable the effects of FF_MIDDLESTARTCHANCE for specific characters whose animations might not be symmetrical.

* FF_MIDDLESTARTCHANCE - has a 50% chance of starting the spr2 or FF_ANIMATE animation halfway in
* FF_SPR2ENDSTATE - if var1 == S_NULL, don't loop, just stop incrementing the frames. Otherwise, go to the state represented by var1.

The former is just something I did for fun, the latter is something that'll come in handy when porting in new-character-moves.

Realised the potential for out-of-bounds memory accessing, so put some limits in place to prevent that from happening.

(skin->availability is a UINT8, so it'll never be negative)

Setup:
* S_SKIN needs an "availability" line. Set to 0 to have always available, otherwise is assumed to be UINT8 unlockable number. If it's a valid unlockable, its name will be copied over with the character's realname.
* Define an unlockable via SOC or hardcode. If you don't want it visible on the Secrets menu, just set its type to None. Everything else is as normal - you can set the conditionset to whatever, objective, height, nochecklist, nocecho...

Also, new default for revitem to match player.dta, and an updated Force Skin netgame option name to reflect the fact it's string based now.