applied patch from Alfred Mickautsch, bugfixes and comments added his test

* xmlwriter.c include/libxml/xmlwriter.h: applied patch from
  Alfred Mickautsch, bugfixes and comments
* doc/examples/*: added his test as the xmlWriter example
* doc/html/ doc/*.html: this resulted in some improvements
* include/libxml/hash.h: fixed an inclusion problem when
  <libxml/hash.h> wasn't preceeded by <xml/parser.h>
Daniel
45 files changed