Generate Python 3 packages by default

[BjarniRunar]

The .deb packaging still bases off Python 2.

As does the single-file "breeder" output. See issue: https://github.com/pagekite/PyBreeder/issues/3

The .deb should be relatively easy to fix, but I'm still on the fence as to whether I should continue to build Python 2 packages as well, and I don't yet know whether I can build packages that will just accept any Python more recent than Python 2.7 or whether I'd need two. Unlike the rest of the Python community, I'm not keen to abandon folks who cannot upgrade for whatever reason.

[BjarniRunar]

The breeder issue is resolved, pagekite.net is as of this evening distributing a bundled .py that works on both Python 2 and Python 3. Still pondering my .deb strategy.

[Mathias-U1F596]

The DEB package from the APT source http://pagekite.net/pk/deb/ should be updated to not depend on the package python-is-python2, because that would uninstall the package python-is-python3, which might be inaceptable.