Updates the pyrax version required.
Adds a config option to set Pyrax identity_type. It is optional once there is other means to set identity_type (like environment variables or config files).
Explain clearly why the config is optional.
Merge remote-tracking branch 'upstream/master' into pyrax-version

Conflicts:
	docs/index.rst
Forgot to change the pyrax version in the setup and docs.
Fixes typo in documentation.
Merge pull request #90 from michelts/pyrax-version

Updates the pyrax version required.