Fix fetching of language codes from loc.gov.

Use the CSV-like file from the site rather than the HTML.
The key in save_polygons is a dummy, so label it as such.
Features are labelled ID 1, not 0.
Compare geometries only to 7 decimal places.

Use shapely's almost_equals() function to compare geometries, as
otherwise 'exact' geometries are missed due to floating point.