readability of fullwidth characters better by not placing cell
boundaries between them unneccessarily

the output is now labelled as XHTML 1.0 Strict, since it does conform
to that DTD. also removed spurious cellpadding and cellspacing from
<div /> markup. also handle non-characters by conversion to
replacement character, and handle more control characters by
conversion to no-break space. finally, switch from &nbsp; to the
equivalent &#160; so that a non-validating XML parser (which is most
of them) can correctly parse this document.

degenerate cases this will lead to incorrectly-displayed tables. i
don't yet have a solution.

and fill the canvas up to the tab stop with it. once that works,
support will be added here (treating it as space.) also, fewer columns
are now generated. apparently generating a minimal number of them
fixes a bunch of the table-layout bugs.

characters and non-unicode codepoints when generating HTML.

optimize by merging cells

cells on any row of the table then the very first row does not use the
cell-merging optimization; this appears to fix the last of the table
layout bugs seen in truecolor.php; also fix the foreground and
background color bugs seen in truecolor.php.

get hopelessly lost.