A deck consists of the following pieces, in this order.  All numbers
are stored as raw binary values; the byte order of all multi-byte
values is always specified explicitly.

- The number of colors used by the deck, ncol (one byte).  Note that
  the format cannot handle decks that use more than 255 colors.
- The number of back designs available, nbacks (one byte).
- The list of colors used.  There are ncol entries in this list; each
   color in the list is three 16-bit numbers, being (in order) the red,
   green, and blue values, on a 0-65535 scale.  Each number is stored
   most-significant byte first.  When colors are referred to elsewhere,
   the color number is always from 0 through ncol-1 and should be taken
   as an index into this list.
- The back designs, in black-and-white.  See below for the layout of
   each bitmap.  There are nbacks bitmaps in this list.
- The card designs, in black-and-white.  See below for the layout of
   each bitmap.  There are 79 bitmaps in this list: first the clubs,
   ace through king, then the diamonds, ace through king, then the
   hearts, then the spades, then generic red, then generic black,
   lastly the joker.
- The back designs, in color.  See below for the layout of each bitmap.
   There are nbacks bitmaps in this list.
- The card designs, in color.  See below for the layout of each bitmap.
   There are 79 bitmaps in this list, in the same order as for the
   black-and-white card bitmaps.

Each image is 71 pixels wide and 96 pixels high.  These numbers are not
stored in the file anywhere.

Each black-and-white bitmap is stored as a string of 96 rows of 9 bytes
each.  The first eight bits of each row are stored in the first byte,
left-to-right MSB-to-LSB; the next eight bits in the next byte,
similarly to the end of the row; the least-significant bit of the last
byte is ignored.  The rows stored consecutively, topmost row first.

Each color bitmap is stored as a string of 96 rows of 71 bytes each.
Each byte holds one pixel of the bitmap, stored as an index into the
list of colors.  The pixels are stored left-to-right within each row;
the rows are stored top-to-bottom within each bitmap.  No attempt is
made to compress the bitmaps by taking advantage of the limited range
of values; the format is intended to be fast to read, not efficient to
store on disk.