Add region to sub-region in output filenames

[rustprooflabs]

Example of the output filename: pgosm-flex-district-of-columbia-run-all.sql

Fine for D.C., but Georgia (in U.S.) is not Georgia (in Europe).

[rustprooflabs]

UPDATE: The idea in this comment is captured in #135.

---

The Docker script currently has a region param and a sub-region param. Should combined them into a single param. This will simplify use by not having an arbitrary difference between a "region" and "subregion".

This would change:

docker exec -it \
    -e POSTGRES_PASSWORD=mysecretpassword \
    -e POSTGRES_USER=postgres \
    pgosm bash docker/run_pgosm_flex.sh \
    north-america/us \
    district-of-columbia \
    8 \
    run-all

TO

docker exec -it \
    -e POSTGRES_PASSWORD=mysecretpassword \
    -e POSTGRES_USER=postgres \
    pgosm bash docker/run_pgosm_flex.sh \
    north-america/us/district-of-columbia \
    8 \
    run-all

Should add a check to script to catch when 4 params are passed and advise the user about the change to 3 params.

e.g. https://stackoverflow.com/questions/18568706/check-number-of-arguments-passed-to-a-bash-script

[rustprooflabs]

Added via #147.