Free Hero Mesh

* 85 to 169 = Heterogeneous run (1 to 85 pixels). Follow by that many
bytes being the pixel values (palette index).

* 170 to 254 = Copy-above run (1 to 85 pixels). Copies the specified
number of pixels from the previous scanline. (If this crosses multiple
scanlines, it continues copying it.)


=== xclass/*.MUL ===

This lump is a "multidependent" lump. The lump name is ignored except for
the MUL suffix, but it is displayed in the picture editor.

The first four bytes are the number of bases and the number of filters in
each of the three filter lists. All of these bytes have the number in the
low 6-bits, and bit7 is set if it is nullable; bit6 is unused and it must
be clear.

After that is the list of bases, each being a null-terminated string,
which must be the name of a .IMG lump without the .IMG suffix.

After the list of bases is the information for each filter chain; first
all chains in the first list, and then the second, and then the third;
null chains are not listed. These records have the format:

* A small-endian 16-bit number, where bit10-bit0 is the length of this
filter chain in bytes, bit13-bit11 is the length of the name in bytes
(not counting the ._- prefix), and bit15-bit14 is the prefix character
(0 if none, 1 if a hyphen, 2 if a underscore, or 3 if a dot).

* The name, not counting the prefix, with no terminator.

After that will be the list of filters in each chain, in the same format
as for DEP lumps but without the base name.


=== xclass/*.WAV ===

A user-defined sound effect. The part of the lump name before the dot is
the name used to refer to it in a class definition file; the exclamation
mark is not included in the lump name.