[xml] typo documentation

[Jean Senellart <senellart systran fr>]

just wanted to mention that there is mismatches in generated documentation around xmlXPathComp structure and 
functions:

----
http://www.xmlsoft.org/html/libxml-xpath.html#XMLXPATHCOMPILE

the "Returns: ..." for xmlXPathCompile is incorrect and comes from xmlXPathEval

xpath.c:
/**
 * xmlXPathCompile:
[...]
 * Returns the xmlXPathObjectPtr resulting from the evaluation or NULL.
 *         the caller has to free the object.
xmlXPathCompExprPtr
xmlXPathCompile(const xmlChar *str) {

----

moreover, the xmlXPathCompExpr structure which is stated as "not public" in xpath.h, appears in the 
documentation at:

http://xmlsoft.org/html/libxml-xpath.html#XMLXPATHCOMPEXPRPTR
 
but the description has no link with the structure (in fact it is the description of static function 
xmlXPathCompileExpr instead of xmlXPathCompExpr which is incorrectly named "xmlXPathCompExpr" in its header) 
- 

xpath.c:
/**
 * xmlXPathCompExpr:
[...]
 */
static void
xmlXPathCompileExpr(xmlXPathParserContextPtr ctxt) {



Jean S.