Big pybugz interface change

[ashtonbatty]

Pybugz 0.10 has apparently been redesigned to use xmlrpc, and as part of the redesign it no longer has the bugz.bugzilla.Bugz class.

This of course makes gitzilla incompatible with pybugz 0.10

( Development of pybugz has moved to http://github.com/williamh/pybugz )

[gtait]

Omnifarious has fixed the missing class in his pull request.
I have also added a pull request to his pull request to support the newer pybugz versions dropping python 2 and Bugzilla changing their authentication over to tokens.