Implementation of abstract base class for recipes

[jeffreyliu]

A python abstract base class (a la Java interface) will serve as the basis for recipes, as well as a reference for implementations in other languages.

User recipes should be classes that extend the abstract base class. Recipes should fork this repo and implement their class.

Which properties and methods should be included the base class is open for discussion. Discussion can happen in this thread, but specific requests and proposals should be opened as separate issues or pull requests.