title: OpenSky Network REST API, response filtered by location
body: <p>Just starting out using the OpenSky Network REST API and am looking for a way to capture aircraft in a particular location.  I can see an api/states/all endpoint, and a way to filter results by receiver using serials=nnn (although the Receiver Availability page only gives the serial number, not the location of the receivers), but is it possible to only fetch aircraft state vectors that match a requested location/range? It could be done in the client of course, but this would help to minimise the API traffic</p>