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.

Meanwhile, a sneaky sneaky for hiding hidden characters further.

Also, I guess CA_SWIM isn't forced into running on water anymore.

* radius - sets the player's radius for that skin.
* height - sets the player's normal height for that skin.
* spinheight - sets the player's spinheight for that skin.
* shieldscale - see http://i.imgur.com/BQ5DhKC.png for justification

Rudimentary SOC shuffling if you add a character with the same name as a previous character to prevent character select from breaking.

More clearly defined handling for replacing character select images. Specifically takes into account whether the hidden character was added in this file or a seperate one.

Also, removed some commented out code regarding character selects, and removed a useless case for R_SkinAvailable().