Swagger: Adding Query parameter to route description.

[bthrall]

We handled this by using enums to extend the Parameter class, and a function to allow easy adding of query parameters.

We're not 100% sure if the query function should be on the subpath as well, though that should be easily enough removed if necessary.

[kiplingw]

Thanks @bthrall. @oktal, if this looks fine to you I'll merge. I'm not really familiar with the integrated Swagger functionality and haven't used it.

[dennisjenkins75]

I'm concerned that this PR directly modifies rapidjson instead of patching it upstream and then properly integrating that fix here. Are you doing a hard-fork of rapidjson?

[bthrall]

I'm concerned that this PR directly modifies rapidjson instead of patching it upstream and then properly integrating that fix here. Are you doing a hard-fork of rapidjson?

It modifies the rapidjson serializer used by Pistache to generate the Swagger JSON.