Added highlight/unhighlight per rule

Added functionality to add highlighting and unhighlighting options to individual rules which will override any set highlighting or unhighlighting in the main settings

ex:

	$('#myform').validate({
		'rules': {
			'name': {
				'required': {
					'highlight': function(element, errorClass, validClass) {
						// Do something ...
					},
					'unhighlight': function(element, errorClass, validClass) {
						// Do something ...
					}
				}
			}
		}
	});