.dat file:
----------
  points
  vectors
  planes

points:
-------
  number of points
    number of points * (x y z)

vectors:
--------
  number of vectors
    number of vectors * (x y z)

planes:
-------
  number of planes
    number of planes * (plane)

plane:
------
  opt type  basecol numcol
     type&128 => midvect
   numvert  numvert * (points)
     type==6 => texthandle  numvert * (x y)

  opt:
    1: show front
    2: show back ?
  128: override mid

  type:
    0: fill
    1: flat shade
    2: rounded shade
    3: mirror
    4: or-fill
    5: texture
    6: transparent texture