Define an "official" extension mechanism

[sampsyo]

Bril is supposed to be extensible, but that extensibility is currently pretty ad hoc: you just add whatever you want to the language. It would be nice to codify some standard way to package up extensions to Bril. There wouldn't need to be a machine-readable description of what an extension consists of, but maybe there should be a way in a Bril program to describe the extensions that the program relies on.

This would require that extensions get assigned (string) names. We would probably want to organize the documentation around a minimal "base" language and individual extensions.