error.php
Contain error handler.
The array key is error code and its value is controller handler. Example:
return array(
'404' => '\Rdb\System\Core\Controllers\Error\E404:index',
'405' => '\Rdb\System\Core\Controllers\Error\E405:index',
);
The class in handler will be automatically add Controller suffix, and the method in handler will be automatically add Action suffix.