compoze TOODs

  - [X] Break monolithic command (version 0.1) into subcommands, and make
        them pluggable via entry points.

  - [_] Use a config file for defaults like:
   
          o 'index_url' lists

          o verbosity

        etc.  Question: where should it go?

  - [_] Fix the 'show' command to get real values from PyPI.

          o Unit tests mock it away too well.

  - [_] Add an 'install' command, which does like 'easy_install' but
        with the following differences:

          o it is willing to check multipe indexes

          o it records the index from which each package was downloaded
            somewhere (do we care?)

  - [_] Add an 'upgrade' command, which checks all installed packages
        in the working set against the specified (or configured) indexes).
