Finish off Acceptable Licensing header

* OSI Code licensing
* Default MIT licensing in the presence of CC
* No derivatives aren't allowed
* Unlicensing isn't allowed

Closes #56 and Closes #116
This bullet doesn't actually assign a default license for libraries. It should probably move to the Acceptable Licensing section.  I would then either add a new bullet here to say what the default library license is, or make it explicit in the previous line that both libraries and scripts get the MIT license as default.