Previously, the schema walker would terminate at a given schema without descending into child schemas. This adds the navigation of those child schemas:

• schemas for object properties (named and unnamed)
• schema for an array's items
• subschemas for oneOf, allOf, anyOf, and not constructions

Move us from convert_case to heck as we have with typify and progenitor for more serde-like case conversion.

Adds a check that enumerated values should be snake_case as with object properties. This makes case conversion for enums consistent regardless of the tagging scheme.