* TODO Restructure simulation
Instead of going for one massive tape with "lines" being programs, go
for 8x8 chunks.

The idea is to draw each individual command in motion instead of the
composite program.  The visualisation will look amazing.
** DONE Refactor brainfuck interpreter
The "catalytic process" (take two programs, concatenate them, execute
the program, split them back) is now completely standalone.  The only
assertions it makes about the input programs is that they are
contiguous.  Essentially the same as our previous implementation.

Now we just need to do the hard bit!
** TODO Refactor simulation
