enable generation of req/rsp bodies given a json schema

[rossajmcd]

[colin-lamed]

This is minimally supported by protean/core/generation/json.clj.

We might want to think about putting it in a separate project and maturing there.

[colin-lamed]

Interesting use of extending the json schema with "faker" data generation: http://json-schema-faker.js.org/#gist/5f81f118fbd4eac01ccacf23a061a8b9

We could similarly refer to the codex from json schema. E.g. reference the codex type for property generation.