Doc fixes.

Doc fixes.
(xml-parse-file, xml-parse-region): Autoload.
(xml-syntax-table, xml-name-regexp): New.
(xml-parse-region): Narrow to region, set syntax-table and
case-fold-search.  Reject fewer valid documents.
(xml-parse-tag): Remove arg END.  Callers changed.
(xml-parse-tag): Use skip-syntax-forward.  Use PARSE-DTD arg
properly.  Don't use buffer-substring-no-properties.  Don't bind
case-fold-search.  Fix syntax for empty elements.  Hoist consing
of end-of-tag regexp out of loop.
(xml-parse-attlist): Remove arg.  Callers changed.  Use
skip-syntax-forward, replace-regexp-in-string, forward-sexp.
Allow non-ASCII names.
(xml-skip-dtd): Remove arg.  Callers changed.  Change matching
code.
(xml-parse-dtd): Grok external DTDs.  Allow non-ASCII.  Don't use
match-string-no-properties.
(xml-ucs-to-string): Deleted.
(xml-substitute-entity): New.
(xml-substitute-special): Use it.
(xml-debug-print-internal): Simplify insertions.
(xml-parse-file): Avoid finding file in xml-mode.