Rename and slightly redefine the default text search parser's "word"

Rename and slightly redefine the default text search parser's "word"
categories, as per discussion.  asciiword (formerly lword) is still
ASCII-letters-only, and numword (formerly word) is still the most general
mixed-alpha-and-digits case.  But word (formerly nlword) is now
any-group-of-letters-with-at-least-one-non-ASCII, rather than all-non-ASCII as
before.  This is no worse than before for parsing mixed Russian/English text,
which seems to have been the design center for the original coding; and it
should simplify matters for parsing most European languages.  In particular
it will not be necessary for any language to accept strings containing digits
as being regular "words".  The hyphenated-word categories are adjusted
similarly.