STAD file format

STAD            *.PAC (high resolution only)

4 bytes         "pM86" (vertically packed) or "pM85" (horizontally packed)
1 byte          id byte
1 byte          pack byte (most frequently occurring byte in bitmap)
1 byte          "special" byte
-------
7 bytes         total for header

? bytes         data

The data is encoded as follows.  For each byte x in the data section:

        x = id byte             Read one more byte, n.  Use pack byte 
                                n + 1 times.
        x = "special" byte      Read two more bytes, d, and n (in order).
                                Use byte d n + 1 times.
        otherwise               Use byte x literally.

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