Tightened some restrictions on Tails carry because right now the looseness leads to edge case noise spam when trying to pick up a player off a rope hang, for example.

Also, the same smoothness changes have been ported over to zoom tubes!

* PF_ITEMHANG -> CR_GENERIC
* PF_CARRIED -> CR_PLAYER
* (mo->tracer == MT_TUBEWAYPOINT) -> CR_ZOOMTUBE
* PF_ROPEHANG -> CR_ROPEHANG
* PF_MACESPIN -> CR_MACESPIN

Just noticed when poking around in dashmodecode that it didn't actually get stopped from running when you were playing in CTF!

# Conflicts:
#	src/p_mobj.c

More slope fixes (aka sorry guys I made another quick SUGOI fix)

Another slopes fix branch!

This branch currently includes a fix for:
* Knuckles gliding into a slope while in 2D mode causes him to try to "climb" on air above them, if the original non-sloped height is higher. Unfortunately he still tries to grab onto places that he can't really climb on, but at least now it's on the slope itself and not in mid-air lol. This issue is encountered in SUGOI's Retro Hill Zone, if you want to check for yourselves.
* Bustable FOF-busting code for both players AND pushables not accounting for slopes
* (Unrelated to slopes): Fix FF_SHATTERBOTTOM FOFs acting like THZ goop when stood on; I added this fix as a bonus because I encountered it in a test map of mine for the bustables fix

(Other fixes may or may not appear here in the near future, I haven't decided yet. Don't wait on me to get in any further fixes before merging, that said)

See merge request !110

Last-minute NiGHTS exiting bugfix

One single-line fix concerning the end of NiGHTS maps. Extremely small, literally zero side effects here, the only reason I'm not committing directly to master (aside from ettiquette) is that I don't have the ability to do so.

* The NiGHTS drone had a single tic of visibility when you hit the goal, which is evident stepping frame by frame through http://gfycat.com/ComplicatedComposedAoudad (the contents of which may or may not make it into 2.2). This is no longer the case.

See merge request !100

DIsable NetPlay on DirectDraw builds

Also disable UPnP support on NONET builds

See merge request !102

Readme rewrite

Our readme.txt is outdated as hell, so I took it upon myself to rewrite it in Markdown. For the sake of simplicity, it links to the wiki for compile instructions. Feel free to commit to the readmerewrite branch if anything should be done differently.

See merge request !111

Optimisation of P_GetMobjGravity (relevant for slopes)

Cleaned up some performance issues in Skytop Zone (2.1.16: THE SUGOI UPDATE) arising from some inefficiencies with P_GetMobjGravity. FPS drops only occasionally to 34 now, which is a big improvement when I was frequently getting 27 in Salt's 15andahalf.exe.

(I also tested in a build of 2.1.16's first release candidate, and was getting drops to 16! So SOMETHING improved since then, but this was the major issue.)

See merge request !109

Record Attack hotfix

Limit damage from http://mb.srb2.org/showthread.php?t=41847, basically.

Also fixed the message popup background because why not

See merge request !107

P_MobjCheckWater now properly accounts for changing heights (skin non-spin height for players, mobj height otherwise) instead of mobj info height.

Also, the particles made via spindashing in shallow water are now located behind the player. This does move the running particles too, but that's okay.

No need to check for under/overflow outside of the spindash code, let's just start at the mindash and not add power if you're over instead.

Revert "Revert "Revitem is saved by tying it to leveltime instead of dashtime, whilst dashtime is now dead.""

This reverts commit 58f815dd.

Revert "Revitem is saved by tying it to leveltime instead of dashtime, whilst dashtime is now dead."

This reverts commit 0852a200.

Some more spindash changes. NOTE that this temporarily breaks the charging aura; if we want to, we can either kill that entirely or re-enable it - but none of the main characters are using it, and Lua makes having a dedicated charging aura irrelevant if the main characters don't use it...

* Spindash sound only plays six times during the charge, equally spaced up until you finish charging.
* Spindash animation speed increase rebalanced.

Fix Knuckles in 2D mode attempting to latch onto air when gliding into a slope. Now he just attempts to latch onto the slope directly (which I'll fix another time, if I can figure out how)

(fix for SUGOI's Retro Hill Zone)

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