Support defining query params as object properties

[crickford]

OpenAPI 3.x supports specifying accepted query parameters as a schema object, which among other things allows API spec authors to accept free-form parameters 🎉

Unfortunately, this does not currently work in OpenAPI Backend - I added a PR here with a failing test suite to demonstrate: #83

Here's an example from the docs:

{
  "in": "query",
  "name": "freeForm",
  "schema": {
    "type": "object",
    "additionalProperties": {
      "type": "integer"
    },
  },
  "style": "form"
}

[elby22]

@anttiviljami @crickford I just made a PR for a similar feature, but using the 'content' property instead of 'style' #120
Hopefully this is helpful in the mean time.