Update is_valid_uri() for checking Unicode letter
Update is_valid_uri() for checking Unicode letter

is_valid_uri() checked only 'in' criteria so that it couldn't check URI which includes Unicode letter other than ASCII zone.
ex. http://ex.com/漢字 should be valid but not
Change: use unicodedata.category for checking Unicode Category, 'Lx' category is valid. If not, use same logic as before.
See: https://www.unicode.org/reports/tr44/#General_Category
RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib