* Add difference tracking tool
* Improve --diff mode for docker_container.
* Improve diffs of sets by ordering the sets.
* Rewrite imports, get rid of HAS_DOCKER_PY_x variables and use docker_version instead.
* Rename container -> active (more generic).
* Add --diff for docker_volume. Change old diff output.
* Add --diff for docker_network. Change old diff output.
* Add --diff for docker_swarm_service.
* Add changelog.
* Add entry for porting guide on docker_network and docker_volume.
* Allow to specify images by hash for docker_container and docker_image_facts.
* flake8
* More sanity checks.
* Added changelog.
* Added test.
* Make compatible with Python < 3.4.
* Remove out-commented imports.
