add parsexml() function, which is a wrapper around the built-in easyxml

add parsexml() function, which is a wrapper around the built-in easyxml
parser. Advantages over xml.nas:             (reviewed and OK'ed by Andy)

- faster (33% ... only. I had hoped for more.)
- more standards compliant
- should support UTF
- I don't have to support it.  ;-)

Usage: parsexml(<path> [, <start-tag> [, <end-tag> [, <data> [, <pi>]]]]);

<path> is an absolute file path, the rest are optional callback functions.

Example:
    parsexml("/tmp/foo.xml", nil, nil, func(d) { print("DATA FOUND: ", d) });