* Clarify the license for files we have signoff on
* Update against the currently signed off files
* Remove unused and not clearly licensed headers
* Replace an #endif I accidentally removed while resolving merge conflicts
Unlike the arduino functions, these don't take abstract pin numbers,
they take pin labels like `B0`. Also, rather than taking very
generic parameter names, these take slightly more descriptive
enum values.
These improve the clarity of code that would otherwise be inscrutable
bit manipulation in tersely named port register names.