Struct representing a call to the PTV API.

Strictly conforms to spec at https://timetableapi.ptv.vic.gov.au/swagger/ui/index.

• :base_url: the base url of the API server, defaults to "http://timetableapi.ptv.vic.gov.au".
• :api_version: the version of the api being called, defaults to "v3".
• :api_name: the name of the resource being called, .e.g. "stops".
• :search_string: id or further path of the resource being called, .e.g "10/route_type/3"
• :params: map of query paramters, .e.g %{stop_amenities: true}