Discontinue use of distribute_setup.py

Most users will already have distribute or setuptools installed. Users
who don't likely have not installed them intentionally.
Add Python 3.3 as a supported version

Include Python 3.3 in the packages trove classifier list as supported.
Also include Python 3.3 as a TravisCI build target.
Don't use PyPI mirrors when installing packages

The implementation of a content delivery network (CDN) for PyPI has
significantly improved PyPI's performance. It is now faster and more
reliable to use the CDN and PyPI's mirrors.
Vendor latest funcsigs

Vendorise the latest version of the funcsigs package inside begins to
avoid a package dependency.
Tweak coverage reports

Use a coverage configuration file to control which files are used when
generating code coverage reports from tests.