Fix cartfile2json.py regex escape sequence

Fix attributions2json.py script

Update scripts to python3 (#7)

* converted python scripts using 2to3
* fixed python3 conversion issues
* implement assertion of non-base64 encoding

Make cell selection and license background color configurable

Make background colors configurable

Fix attributions2json to work without GITHUB_ACCESS_TOKEN being set

Merge pull request #5 from kayak/features/additional_attributions

Allow adding additional attributions

Update to Swift 4.2

Add support for readable content width

Removed bundled common licenses