Draft: MapSetup Hook

The MapSetup hook executes at the beginning of the P_AdjustLevelSettings function, which gets called after the raw data for the map has been loaded, but before the blockmap gets loaded or created. After the MapSetup gets called, then some mapheader_t variables that previously took effect before the raw data gets loaded will now take effect in the P_AdjustLevelSettings function instead to allow for more mapheader_t variables to be edited in the MapSetup hook. Also, linedef specials of existing linedefs can be changed in the MapSetup hook, but the only reason that other linedef properties cannot be edited in the MapSetup hook is due to SRB2 not building nodes at all.

Test file: mapsetuphooktest.lua