font: halfwidth redesign of circled alphanumerics

Most terminals do not display wide glyphs in this range.  Prefer resizing to
4-5px width.  Keep to 7px height to keep a mostly circular appearance;
parenthesized characters can be slightly taller.

Creative solutions required include stacking two-digit numbers to fit, and
merging vertical borders for double circled glyphs.  Circled digit zero
U+24EA was given an irregular shape to distinguish it from letter O U+24C4.