feature/dynamic_response_fields :: Dynamically generates response_fields

In documenting an api with dozens of endpoints, each with dozens of response fields, the manual setting of response fields is tedious.  With proper fixtures/factories/fabricators, there is no need to manually specify the response fields. The resulting http response body should be correct.

Introducing, Dynamic Response Fields. This commit enables the ability to dynamically generate response_fields from actual http response body, including nested attributes with scope.  Manually supplied response_fields take precedent.  Dynamic response fields are disabled by default, but can be enabled through the following configuration:

    config.dynamic_response_fields = true

Works out of the box with Raddocs.

Added Bonus:

The side benefit of dynamic response fields is that for the documentation to be accurate, the test suite must be accurate.  The fixtures/factories/fabricators must accurately represent the live data. Therefore,  improving the documentation, improves the test suite.
Very good point.