Docker-squash

- 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

Fixed issue with installing from PyPi

- New CLI options
- Layers and squash merged into one tool
- Available now in PyPi: `pip install docker-scripts`