Add clear() function.

Signed-off-by: Paul Brook <paul@nowt.org>
Refactor demo sketch

Signed-off-by: Paul Brook <paul@nowt.org>
Merge worm into new demo framework

Signed-off-by: Paul Brook <paul@nowt.org>
Demo time limit

Signed-off-by: Paul Brook <paul@nowt.org>
Define and use CUBE_SIZE.

Signed-off-by: Paul Brook <paul@nowt.org>
Add rain demo

Signed-off-by: Paul Brook <paul@nowt.org>