The backend responses are now read in one place and the functions just
read the data. The protocol level will now handle the packet gathering
process and the authentication part just inspects the data.
Backend connections now load authenticators when they are being
connected. In the future, this enables the use of authentication modules
for backend connection.
The DCB error messages now log the type of the DCB and the remote address
in addition to the system error message. The file descriptor and memory
address are no longer printed in the error message as they are not useful
to the end user. The fd and address are now logged at debug level with a
more verbose error message.
Each protocol module now resides in a subdirectory of its own.
The name of the subdirectory is the same as the name of the
library in the module's CMakeLists.txt file.
