Libxmljs async sax parser example

[Marco Rogers]

Several people have asked about async parsing in libxmljs. The sax
parser works fine. But maybe not everyone knows how it works. I
spent some time on an illustrative example.

http://gist.github.com/484083

This is using the push parser. The normal pull parser works the same,
but you don't have to manually feed in the file data. Feedback is
always appreciated.

:Marco