Allow factory methods to be called with a factory constructor

[cameroncondry]

Now that the ability for factory methods to reference the DI container exists (#13), can we allow factory methods to be called with the existing class method using a factory callable constructor? I would image the functionality of the new constructor method would be similar to how the current "addMethodCall" works.

Example:

class MyClassFactory
{
    public static function createMyClass(Container $di)
    {
        return $di->get(MyClass::class);
    }
}

$di
    ->register(MyClass::class, 'class')
    ->toClass(MyClassFactory::class)
    ->setConstructor('createMyClass', [$optionalArg1, $optionalArg2])
;