Refactor XML library to support names that don't conform to XML

Refactor XML library to support names that don't conform to XML
Namespaces.  This was extensive mostly because there was a built-in
assumption that all XML names could be mapped to QNames, which isn't
true.  Some incompatible changes:

renamed:
    XML-NAME-QNAME ==> XML-NAME->SYMBOL

eliminated:
    MAKE-XML-NAME-HASH-TABLE
    XML-NAME-HASH
    XML-NAME-QNAME=?
    XML-NMTOKEN-STRING
    XML-QNAME-STRING