cutext: Unicode and Text Handling

Modules
	cutext/bufsource.h: Buffer Source
	cutext/encoding.h: Unicode Encodings
	cutext/lsource.h: Wide Character Source for Lexical Analysis
	cutext/sink.h: Text Sink
	cutext/source.h: Text Source with Optional Lookahead
	cutext/wccat.h: Unicode General Categories
	cutext/wctype.h: Unicode Character Types