Commands for fetching incremental updates

[Morgon]

GeoNames builds two files each day, modifications-$date.txt and deletes-$date.txt, where $date is the previous day. This allows for incremental updates without having to rebuild the entire table.

Having commands that download/store those text files in the meta/geonames directory, as well as separately applying those stored updates incrementally (and delete when applied, perhaps?) would be wonderful for this purpose.

Additionally, with #3, being able to specify feature types would help ensure that no attempts to update or add unneeded (or non-existent) data are made.