Adds func GeocoderLocal to pkg openstreetmap

[jriquelme]

GeocoderLocal constructs an OpenStreetMap geocoder using a custom installation of Nominatim.

[dougnukem]

Thanks for the contribution.

I'd prefer if the method was more reflective of it's use (not just for local testing GeocoderLocal(nominatumURL string) e.g. GeocoderWithURL(nominatumURL string)

Or we could just have the default Geocoder constructor accept the URL as a param:

// Endpoints for Production Nominatum API base URLs
const (
    ProductionURL = "https://nominatim.openstreetmap.org/"
)

// Geocoder constructs OpenStreetMap geocoder
func Geocoder(nominaturmURL string) geo.Geocoder {
    return geo.HTTPGeocoder{
        EndpointBuilder:       baseURL(nominatimURL),
        ResponseParserFactory: func() geo.ResponseParser { return &geocodeResponse{} },
    }
}

Then to use it it'd just be:

var geocoder = openstreetmap.Geocoder(openstreetmap.ProductionURL)

[jriquelme]

GeocoderWithURL(nominatimURL string) seems good to me.

Regarding to the second option, I would prefer a new function, to not break existing code due to the signature change of openstreetmap.Geocoder().

[dougnukem]

👍 GeocoderWithURL(nominatumURL string) works for me, might be nice to refactor the implementation of the original constructor just to avoid duplicating code.

But that can be done in a followup PR.