Pan African is not a valid BCP 47 language tag

[bramstein]

Hi!

I recently updated our local clone of the speakeasy repository and got a failure on validating the language tags. Before the changes in #43 all speakeasy files used valid BCP 47 language tags. Unfortunately panafrican is not a valid language tag. Is there a way to fix that, or perhaps my assumption the language tags should be valid is incorrect?