PATCH: deprecation warnings for unreasonable charnames

PATCH: deprecation warnings for unreasonable charnames

Prior to now just about anything has been legal for a character name in
\N{...}.  This means that legal code was broken by having \N{3,4} for
example mean [^\n]{3,4}.  Such code doesn't come from standard
charnames, but from legal custom translators.

This patch deprecates "unreasonable" names.  handy.h is changed by the
addition of macros that taken together define the names we deem
reasonable,  namely alpha beginning with alphanumerics and some
punctuations as continuations.

toke.c is changed to parse each name and to raise a warning if any
problematic characters are found.

Some tests and diagnostic documentation are also included.