Add support for receiving fragmented STOMP frames

When using the overTCP method in node.js, the data callbacks do not maintain the message boundaries in the STOMP frames.  Any messages that are slow to be received or large are fragmented at arbitrary points in the frame.  In addition frames can be fragmented in a WebSocket context when the frame size exceeds the maximum frame limit.

This change adds support for receiving any fragmented message, by defragmenting at the point the message is unmarshalled and therefore fixes both issue #55 and #68.