[luatex] documentation on builtin utf library

[Arthur Reutenauer]

> could you please point me to some documentation on the selene utf
> library that is mentioned in the luatex reference?

  I don't think there is any, but the test file that comes with the library
sources should provide some indications, as well as the general idea that the
unicode.ascii, unicode.utf8 and unicode.grapheme each provide the same
functions as the standard string library (i.e., unicode.utf8.gmatch is a global
match function for UTF-8 strings just like string.gmatch is for ASCII strings,
etc.)

	Arthur