Change country_codes to countrycodes

[francisbarton]

Also change address_details to addressdetails but I haven't tested that.

As documented at https://nominatim.org/release-docs/develop/api/Search/#parameters

Compare:

• https://nominatim.openstreetmap.org/search.php?q=halifax&limit=3&country_codes=gb,us (result includes Halifax, Nova Scotia, which ought to be excluded: therefore this query is equivalent to simply: https://nominatim.openstreetmap.org/search.php?q=halifax&limit=3)
• https://nominatim.openstreetmap.org/search.php?q=halifax&limit=3&countrycodes=gb,us (successfully excludes Halifax, Nova Scotia, as intended).

Haven't made changes to the params to osm_search because obviously this would break compatibility with existing usage.

I also added into the script an example of how to use country_codes, because I took a long time to work out the proper syntax for that myself! Thought it might be helpful to others.