bmp block allocation glyphs

Overview of BMP blocks similar to <http://sheet.shiar.nl/charset/unicode>
each represented by an identifying glyph copied from Unidings v9.19
<http://users.teilar.gr/~g1951d/Unidings.pdf> by George Douros.

Characters align neatly to 0x40 code points, preferring every other column
if feasible, but keeping various smaller (rtl, brahmic) scripts for now.
Silently break positions between U+3400 and U+A400 because these only
contain cjk and yi with usually uniform font coverage.