Convert camelCase keys to snake_case variable names

Javascript and hence JSON have a convention of using camelCased key names, whereas Python by convention uses snake_cased variabled names. This causes problems with QuartSchema as by default the JSON key name is the variable name. To convert between pass convert_casing=True when initialising QuartSchema, e.g.,

QuartSchema(app, convert_casing=True)

This will require that JSON and query string sent to the app is camelCased and will ensure that JSON returned from the app is camelCased and that the OpenAPI schema is correct (also camelCased).