This way we get updated versions automatically (referencing "master"
required manually deleting the downloaded archives and the unpacked
directories). It also allows switching versions when working in different
branches (note that REV can also be set to a commit ID, e.g. to test
changes before tagging them later and merging the branch).
Apparently, djangorestframework-camel-case, in the referenced version,
uses `six` but does not itself require/install it (later versions removed
Python 2 support altogether).
Tobias Brunner