bpo-32820: __format__ method for ipaddress (#5627)

* bits method and test_bits

* Cleaned up assert string

* blurb

* added docstring

* Faster method, per Eric Smith

* redoing as __format__

* added ipv6 method

* test cases and cleanup

* updated news

* cleanup and NEWS.d

* cleaned up old NEWS

* removed cut and paste leftover

* one more cleanup

* moved to regexp, moved away from v4- and v6-specific versions of __format__

* More cleanup, added ipv6 test cases

* more cleanup

* more cleanup

* cleanup

* cleanup

* cleanup per review, part 1

* addressed review comments around help string and regexp matching

* wrapped v6 test strings. contiguous integers: break at 72char. with underscores: break so that it looks clean.

*  's' and '' tests for pv4 and ipv6

* whitespace cleanup

* Remove trailing whitespace

* Remove more trailing whitespace

* Remove an excess blank line