Bump to version 0.7.2-NB

WebsocketRailsClient++ (v0.7.2-NB)

This version with the abbreviation NB is a non blocking message handler version. This NB version handles every incoming message in an own thread. Why? If the incoming message gets dispatched and executes a callback, the callback can take an unknown amount of time. This blocks the complete incoming message handler. So, packages like ping-pong may be lost and the connection closes.

Changelog

• Solves blocking message handler.
• Solves many bugs.
• Solves segmentation fault if using channel subscribe and callbacks.
• Adds unsubscribe function with callbacks.
• Code rework.