weight of the xor of old and new frames, and switch to setting the
new byte directly instead of xor'ing, to improve efficiency of decoder.
Instead of iterating in a fixed order by target byte then page, at
each step compute the next change to make that would maximize
cycles/pixel, including switching page and/or content byte.
This is unfortunately much slower to encode currently but can hopefully
be optimized sufficiently.
bytestream by prioritizing bytes to be XOR'ed that have the highest
hamming weight, i.e. will result in the largest number of pixel
transitions on the screen.
Not especially optimized yet (either runtime, or byte stream)
