By checking the plugin's API reference, it looks like all you need to do is call .cycle("toggle")
to toggle pausing/resuming the slideshow.
I edited your code and included the following at the bottom of your JavaScript.
$('#slideshow img').click(function() {
$('#slideshow').cycle('toggle');
});
That makes it so whenever an image is clicked on within the slideshow, it will pause.
Check out this JSfiddle - http://jsfiddle.net/skoshy/ka2Xs/20/