WARNING: This method may be slow! It is advisable to use another method if one is available, for instance, using ORDER BY in an SQL statement to create and add the objects in order.
The $element parameter can specify either an attribute or a method of the objects in the collection. Methods should be named in full e.g. "method()".
Although this uses the PHP function usort(), the array keys are preserved.
The constants SORT_OBJECTS_ASC and SORT_OBJECTS_DESC are provided to set the $sort_direction parameter.
If you set $astime to true, the method will try to use PHP's strtotime() function to attempt to convert strings into time, allowing you to sort dates in the expected order. You must ensure that all data will convert to strtotime, or that data will be evalutated as false!
Example:

class Employee {
public $name;
public function __construct($name) {$this->name = $name;}
public function getName() {return $this->name;}
}

$employees = new Employees; // create collection object
$employees->add(new Employee('neil'));
$employees->add(new Employee('David'));
$employees->add(new Employee('Shane'));

// order by name attribute
$employees->sortObjects('name');
// new order: David, neil, Shane

// order by method return, and case sensitive, and passing a single parameter of true to the method
$employees->sortObjects('getName()', Employees::SORT_ORDERS_ASC, false, array(true));
// new order: David, Shane, neil