Create test/ directory and basic Makefile template
Remove uncertain, commented out Unicode-related tests

The experienced behaviour is in fact correct, since "十" nor any other
Chinese numeral is considered a numeral by isdigit(), which only cares
about alternate /glyphs/ for the plain old decimal/arabic system.

The Chinese numbering system has its own composition rules (e.g. "2" is
written "二" - i.e. two horizontal strokes, "1" is written "一" - i.e.
single horizontal stroke, but "21" is not written "二一").