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
> I think that this should only apply if a content-only license is the only license specified. People may wish to dual license, e.g. If a script contains embedded content such as images.

You just summarized that single sentence in two sentences.