Description:
------------
When calling Stomp::readFrame on an instance of the Stomp class, it would be helpful if a custom class which extends StompFrame is returned.

Example - Stomp::readFrame accepts a parameter of which class to return.

<?php
class CustomFrame extends StompFrame {}

/* setup client and get to a point where reading frame is required */
if ($client->hasFrame()) {
    $frame = $client->readFrame('CustomFrame');
}
?>

There are other places where the Stomp client could be told which class to return by Stomp::readFrame, like the constructor or when subscribing, but defining the class in Stomp::readFrame would give the most flexibility.

Expected result:
----------------
Class returned by calling Stomp::readFrame is an instance of CustomFrame