Adds function handler
@param {Function} fn Handler
@param {Object} options Handler options. Possible values are:<br><br>
<b>order</b> : (<code>Number</code>) – order in handler list. Handlers
with higher order value will be executed earlier.
function(fn, options) {
			this._list.push(_.extend({order: 0}, options || {}, {fn: fn}));
		}