New tag 00.21.00 - Changed name and signature of the backend identifier function to plain C - Added example how to register a new backend type - Removed closing of a Backend when the Device goes out of scope. It does not fit the new sheme that the factory is giving the same backend instance to all devices. - Some fixes to experimental features 'readAsync()' and 'readAny' - Removed CLANG compiler warnings - Fixed namespace ambiguity (gcc 6.3 was complaining)