improving some documentation comments found and fixed a mem leak with

* tree.c: improving some documentation comments
* xmlregexp.c: found and fixed a mem leak with python regression tests
* doc/*: rebuilt the doc and the API XML file including the
  xmlregexp.h xmlautomata.h and xmlunicode.h headers
* python/generator.py python/libxml2class.txt python/libxml_wrap.h
  python/types.c: added access to the XML Schemas regexps from
  python
* python/tests/Makefile.am python/tests/regexp.py: added a
  simple regexp bindings test
Daniel

python/types.c

@@ -505,3 +505,21 @@ libxml_xmlParserInputBufferPtrWrap(xmlParserInputBufferPtr buffer)
                                      (char *) "xmlParserInputBufferPtr", NULL);
     return (ret);
 }
+
+PyObject *
+libxml_xmlRegexpPtrWrap(xmlRegexpPtr regexp)
+{
+    PyObject *ret;
+
+#ifdef DEBUG
+    printf("libxml_xmlRegexpPtrWrap: regexp = %p\n", regexp);
+#endif
+    if (regexp == NULL) {
+        Py_INCREF(Py_None);
+        return (Py_None);
+    }
+    ret =
+        PyCObject_FromVoidPtrAndDesc((void *) regexp,
+                                     (char *) "xmlRegexpPtr", NULL);
+    return (ret);
+}