This is the first of many steps designed to reduce gint's reliance on
the FX9860G and FXCG50 macros by describing the compile target more
symbolically. The goal is to allow both for g3a compilation of fx-API
code and for a potential CP port.
This change modifies the font_t type to replace the concept of charset
with a more generic list of non-overlapping Unicode blocks defined by a
starting code point and a size.
It also takes advantage of the assembly feature of fxconv, introduced
for libimg long after the first version of topti, to support pointers in
the converted structure rather than having to tediously compute offsets
within a variable-size structure.