Missing /products/{productId}/parameters endpoint

[jkeifer]

The spec has added a new required endpoint, GET /products/{productId}/parameters. Rather than including product parameters as part of the Product object returned from GET /products/{productId}, the parameters should now be returned separately as a jsonschema object from the new aforementioned endpoint.

[parksjr]

I think we are addressing this in #80, right? Instead, though, it's: GET /products/{product_id}/constraints

If that isn't correct let me know and I'll remove the linked PR