Docker-squash

- Uses `AutoVersionClient` to not fail when there is a mismatch between version of `docker-py` and the server
- Does not fail with stacktrace when no image is specified
- Version information is now printed on execution

- Make sure we do not include `./` as the prefix for files in the squashed tar, thanks TomasTomecek!
- Squashed layers has now a proper `VERSION` file
- Fixed metadata size parameter

- Work on correct image JSON metadata (28)

- Reworked the squashing algorithm
- Make loading image optional, use `--output-path` to specify a path where the image should be stored as TAR file instead loading to Docker daemon
- First unit tests added
- First integration tests added
- Docker timeout bumped to 10 minutes, now it's configurable using `DOCKER_TIMEOUT` environment variable
- Fixed issue where on AUFS the marker files that were added at the end failed to load the image into Dameon (22)

- Make sure it can work with older `six` package
- Add `--version` switch

- Support for Python 3
- Fixed 13 where non-string PAX headers could fail squashing