Merge pull request #54 from shoonoise/master

Fix bumpversion
clarify if/else logic in Image.getfullrepository
more debug logging when generating Shipment
Container: override __getstate__ instead of __setstate__ to allow recursive save
port specifications replaced with Interfaces
refactoring: added refs to parent to all child objects
fixed --clear-cache handling
added "shipment objgraph" command that dump object graph
fixed tests
added "volumes" command group
added "interfaces" command group
added "ships containers" command group
Bump version: 8.1 → 9.0
Interface class renamed to Door
Bump version: 9.0.0 → 9.1.0
setup.py: added psutil dependency
tox.ini: install dominator[full] for tests
Container: added "doors" property
fixed command docstrings
"containers" command group renamed to "container"