1.0.3: Preparations for releasing on pypi.python.org

* setup.py: Switch package name to "pxpx"; just "px" wasn't available on Pypi
* README: Covert to Restructured Text as used on Pypi
* setup.py: Use README.rst as the "long_description"
* setup.py: Add Pypi classifiers
* setup.py: Add missing "ptop" entry point

In addition to this, we now treat "node" as an interpreter when parsing command
lines. That's really unrelated, but slipped in here anyway.