Merge branch 'flat_alignment_revamp' into 'master'

Revamps of several dated linedef type effects

Felt like being productive so made some things I hate suck less.

Linedef type 7 (flat alignment) now works as follows.
* Linedef angle (from v1 to v2) is flat angle.
* Origin of flat is manipulated to match v1's coordinates - unless ML_NOKNUX is flagged, in which case uses frontside x and y offsets as flat offsets instead.
* ML_NOSONIC prevents changing floor.
* ML_NOTAILS prevents changing ceiling.
* Both of the above flags at once prints a warning.
* (THZ and probably a few other maps need updating.)

Linedef type 540 (friction) now works as follows.
* Controlled by x offset instead of length - offset of -100 is maximum iciness, offset of +483(!!!) is the maximum sludginess BUT things are scaled such that +100 is about the maximum sludginess any reasonable human being would want in a level, 0 is ORIG_FRICTION)
* Not reliant on a sector special to function (can be applied solely by tag to in-map sectors or solid FOF control sectors)
* Uses less memory, perform less calculations, and not bug out objects which just happen to use movefactor for something
* PHYSICS CHANGE: Low friction surfaces actively impede your acceleration (and make your animation speeds faster to give off that Looney Tunes out-of-control effect)
* (ACZ and Frozen Hillside needs updating.)

Sector types 1 and 3 in section 3 no longer do anything.

Linedef type 3 (zoom tube) now works as follows.
* Abs of frontside x offset is speed in units of FRACUNIT/8.
* Abs of frontside y offset is waypoint sequence number.
* Effect 4 flag rotates the player to match the waypoint direction (same as before).
* (ERZ needs updating.)

Linedef type 11 (rope hang) now works as follows.
* Abs of frontside x offset is speed in units of FRACUNIT/8.
* Abs of frontside y offset is waypoint sequence number.
* Effect 1 flag makes rope transfer one-way. (same as before)
* No climb flag makes rope static. (same as before)
* (ACZ and maybe ERZ need updating.)

Linedef type 258 (laser) is almost the same as before, but has altered functionality.
* Its flashing is less obnoxious. (56.25% to 68.75% instead of 100% to 0%, at half the speed)

Linedef type 14 (Bustable block parameters) is new, and works as follows.
* Tagged to the control sector of a block that is likely to be busted (via executor or collision, doesn't matter)
* Concatenation of frontside textures is MT_ object type to spawn, defaults to MT_ROCKCRUMBLE1 if not present
* Sound played when being busted is object type's activesound
* Frontside x offset is spacing (in fracunits) of spawned particles, defaults to 32<<FRACBITS
* Frontside y offset is the fuse of spawned particles in tics, defaults to 3*TICRATE, if set to -1 fuse is not set
* Effect 1 flag makes particles "fly out" horizontally and vertically from the center of the FOF

Sector types 7 through 15 in section 3 no longer do anything.

Linedef type 250 (Mario Block) is almost the same as before, but has new functionality and is slightly different in another way.
* No Climb flag turns it into a brick block (set on Custom FOF via presence of FF_SHATTERBOTTOM - busts when hit from the bottom, player hits their head/fist/whatever, no more upwards momentum)
* Effect 1 flag makes it an invisible block (set on Custom FOF via absence of (FF_SOLID|FF_RENDERALL|FF_CUTLEVEL) - intangible from every side except the bottom. Becomes visible and tangible when it's hit once)
* Only updates side textures when moving down or stationary, not whilst moving up - more fidelity to the source material, less processing on the CPU, everyone wins.
* If FOF master linedef has a backside, then: [If there's items in it the FOF's flats are set to that of the backside sector's ceiling, otherwise the floor.] Otherwise, no flat change.

Linedef type 4 (Speed Pad parameters) now works as follows.
* Frontside x offset is speed in fracunits.
* Effect 4 flag doesn't center the player. (same as before)
* Effect 5 flag sends them off in rolling frames.
* Frontside upper texture is sound to play on launch, defaults to sfx_spdpad when not given

Sector type 6 in section 3 no longer does anything.

Object type 757 is changed as follows, and no longer works on its own - see Linedef type 15 for more details.
* Tag via its angle field
* Number of objects to spawn per tic around it via its z field, if zero then just spawn at center
* Is flipped if given MTF_OBJECTFLIP.
* (ERZ and Seraphic Skylands - if we use that map - needs updating)

Linedef type 15 (Fan particle spawner parameters) is new, and works as follows.
* Tag is tag of object(s!)
* Object type set via concatenation of frontside textures, MT_PARTICLE is default
* The length of the linedef is the radius the particle is spawned out (zeroed if z field is 0)
* Frontside x offset is speed upwards
* Frontside y offset is number of degrees to turn each tic (zeroed if z field is 0)
* Frontside floor and ceiling heights are the heights in which the particle is bound through some fun mathematics

A_ParticleSpawn is changed, too.
* Object type is now changed through actor->threshold instead of var1 to support Linedef type 15.

Test executable uploaded at /toaster/srb2win_branch_flatalignment.exe on the ftp.

Test file uploaded at /toaster/flatalignment.wad on the ftp.

Breaks compatibility with 2.1 so put in internal.

See merge request !29