flatten screen ram buffer filling logic to improve timing.
make fastio read and write lines visible in serial monitor register display.
slightly clean up memory access. still currently broken.
(memory reads via monitor work, but writes write all over IO,
rather than the single directed location, wherever that may be.)
try to further flatten glyph_chardata fetching.
further logic flattening.
fix typo
fix stupid variable initialisation bugs.
remerge memory write path.