Remove unneeded variables, simplify code
Simplify control flow
Merge branch 'rel-0.7.x' of https://github.com/drkjam/netaddr into rel-0.7.x
Mark Python 3.3 and 3.4 as supported (ticket #75)

Also replace link to packages.python.org (HTTP 301 Moved Permanently)
and replace all http links with https links.