Allow to set the quoting character of an xmlWriter

It's otherwise impossible to set the quoting character of
attribute values of an xmlWriter.

include/libxml/xmlwriter.h

@@ -471,6 +471,10 @@ extern "C" {
         xmlTextWriterSetIndentString(xmlTextWriterPtr writer,
                                      const xmlChar * str);
 
+    XMLPUBFUN int XMLCALL
+        xmlTextWriterSetQuoteChar(xmlTextWriterPtr writer, xmlChar quotechar);
+
+
 /*
  * misc
  */

xmlwriter.c

@@ -4609,6 +4609,26 @@ xmlTextWriterSetIndentString(xmlTextWriterPtr writer, const xmlChar * str)
         return 0;
 }
 
+/**
+ * xmlTextWriterSetQuoteChar:
+ * @writer:  the xmlTextWriterPtr
+ * @quotechar:  the quote character
+ *
+ * Set the character used for quoting attributes.
+ *
+ * Returns -1 on error or 0 otherwise.
+ */
+int
+xmlTextWriterSetQuoteChar(xmlTextWriterPtr writer, xmlChar quotechar)
+{
+    if ((writer == NULL) || ((quotechar != '\'') && (quotechar != '"')))
+        return -1;
+
+    writer->qchar = quotechar;
+
+    return 0;
+}
+
 /**
  * xmlTextWriterWriteIndent:
  * @writer:  the xmlTextWriterPtr