Tidy up the formatting of the character classification functions, including
improving the documentation. Furthermore, change the "isvalid" function into
more general "isucs4", "isutf32" and "isutf16" functions, which is another
ABI change.
This type doesn't bring anything over an int and requires some special
handling (e.g. including the right headers). Just drop it and use int, C
programmers will understand!
Laurence Withers