(xml-ucs-to-string): New function to convert Unicode codepoints to strings.

(xml-ucs-to-string): New function to convert Unicode codepoints to strings.
Uses decode-char (mule.el) if available.
(xml-parse-tag, xml-parse-attlist, xml-skip-dtd, xml-parse-dtd,
xml-parse-elem-type): Use ' \t\n\r' instead of '[:space:]'.
(xml-parse-attlist): Added attribute normalization.
(xml-parse-tag): Replace "\r\n" and "\r" with "\n".