release-0.3.1

• Reworked test framework to rely on tox's test generation features. This allows for individual test cases to be run on a per provider basis.
• Added more OpenStack swift config options (OS_AUTH_TOKEN and OS_STORAGE_URL)
• Added supports for accessing EC2 containers with restricted permissions.
• Removed exists() method from object store interface. Use get()==None check instead.
• New method (img.min_disk) for geting size of machine image.
• Test improvements (flake8 during build, more tests)
• Patch for binary file handling in openstack
• Misc bug fixes and improvements
• Changed library to beta state
• General documentation updates (testing, release process)