Netconf-client

Thanks to synther !

This release requires Python 3.6.2 or later.

It also includes a small bug fix (see https://github.com/ADTRAN/netconf_client/pull/15)

change: Logging exceptions raised by the pretty formatter are caught,
and an error message and the plain NC message are logged instead.
speed: A little bit more speed improvement (long messages).

Co-authored-by: Wolfram Burkhardt wolfram.burkhardtadtran.com