Add PureXML.Parsing.XMLCharacter as the single source of truth for character
classes, implementing the exact XML 1.0 (Fifth Edition) Char, NameStartChar, and
NameChar productions as public scalar predicates, plus isValidName. The scanner's
name recognition now delegates to these exact ranges (replacing a loose isLetter
check) and handles precomposed and combining-mark names. Closes#35.
Reimplemented from the XML grammar; no upstream code copied. 4 tests; 98 total.
