"""ANSI / CP437 "BBS art" output.

Not a real machine -- this renders the image as classic 16-colour ANSI text art
suitable for display on a bulletin board system (or any ANSI/CP437 viewer).  Each
character cell is the CP437 upper-half-block (``0xDF``) with the foreground colour
painting the top pixel and the background colour the bottom pixel, so one 80-column
row of text is two rows of freely-coloured pixels.  Sixteen EGA/VGA colours are
available for both halves (bright backgrounds use "iCE colours"), so the picture is
just a free 16-colour image at 80 x (2*rows).
"""