deprecate ncvisual_geom() in favor of new ncvisual_blitter_geom(), which allows caller to get the blitter used. replace the checks and calculations in ncvisual_render() with a call to ncvisual_blitter_geom(), unifying the two paths (and eliminating several bugs in the unloved ncvisual_geom()).
- update NcCell documentation according to last release.
- implement NcCell.load method.
- bonus: remove old "width bias" info from the python bindings.
- bonus: add some (commented out) profile settings to Cargo.toml.
Some EGCs are more than 2 columns (wcwidth() never returns more than 2, so far as i can tell, but when multiple characters combine, we use the sum). An example would be ကြေ (Myanmar) which occupies three columns over the course of three characters. Track the width (biased by 1) in cell->width, taking over 8 bits from cell->reserved. Use this width in rasterization. Closes#1203.