Rename Python library to zpmlib

This allows us to better distinguish between the script and the
library behind it.
Remove unnecessary sys.path hack

Now that the main driver script is in the zpmlib's parent directory,
it can import zpmlib directly. When the script and library are
installed system-wide, this import will still work.
zpm: clean up unused imports
Add simple setup script
Merge pull request #9 from mgeisler/distutils

Add setup.py and move zpm code to `zpmlib` package