Merge pull request #76 from pthedinger/master

Adding support for using GUIDs to select End Station
Re-work accesses to the entity and config descriptors to prevent segfaults when the end station had not been fully enumerated.
White space tidying.
Fix segfaults on shutdown. Ensure that the system is shut down in a determinist order that means state is not used after it is freed.
Fix lock-up. Prevent case where non user-generated packets incorrectly lock semaphore waiting for response.
Merge github.com:audioscience/avdecc-lib