namespace.py include colon in ALLOWED_NAME_CHARS
namespace.py include colon in ALLOWED_NAME_CHARS

This commit updates the behavior of is_ncname and
split_uri to match the behavior described here:
https://www.w3.org/TR/html4/types.html#type-name
(found via
http://stackoverflow.com/questions/2053132/is-a-colon-safe-for-friendly-url-use).
This results in the correct splitting of uris such as
http://neurolex.org/wiki/FMA:7191. Extra note that not
all user agents conver : -> %3A since they are not
required to by the spec (RFC3986).

RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib,RDFLib/rdflib