DOC : README tweaks
removed InterfaceRegistry

new-style objects already keep track of subclasses (via
`baseKlass.__subclasses__()`).
INST : also install sub-modules
ENH : finished cleaning out registry code
ENH : re-worked how md about arguments are returned
ENH : added draft of np backed dist source/sink
INST : updated setup.py + import magic
EXP : added example Tool