Fieri Workers: make more clear the differences that make a difference

[robbkidd]

With 4 quality metric workers implemented in Fieri, there is some duplication between them:

• processing cookbook and cookbook_version data responses from the Supermarket API
• posting back an evaluation (quality metric result)

In an effort to help community members more easily contribute a quality metric implementation, the workers should receive some renovation to:

• reduce the duplication of processing information
• make clear what is different about a metric worker and what is similar
• documentation (e.g. rdoc comments) within the refined worker implementations to give guidance to new implementations