[cairo] Truchet Tilings

[Lawrence D'Oliveiro]

Just did a new addition
<http://default-cube.deviantart.com/art/Truchet-612095093> to my
Qahirah Examples collection, showing the power of Cairo+Python. This
one was inspired by an article on MathWorld.

It seems Truchet tiles are normally considered as something to be
rotated to different orientations. However, it is better to think of
them as undergoing a combination of reflections about the x- and
y-axes. This lets you generalize to non-square tiles, and to
higher-dimensional tiles.