Differences from Lua version:
- Does not set cusval
- Does not have individual states for pulley, hook
- Simply sets sprite on S_INVISIBLE
- Does not do P_CheckPosition, sets Z directly
- Does not spawn chain visual every tic
- Spawns a single object and vertically stretches it to
the correct length
- MT_IPULLUP has MF_SCENERY and a short-circuiting
thinker, also MF_NOBLOCKMAP so there is never any
collision against it (it is a controller)
- MT_PULLUPHOOK has MF_NOCLIP to avoid extra collisions
while moving