Add GEOMETRIC_DATA_DIR environment variable

[xylar]

This is the default location to look for geometric data if it is set. The ability to set this variable will enable optionally packaging the data with the conda package.

[pep8speaks]

Hello @xylar! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2020-03-04 04:48:48 UTC

[xylar]

Testing

I made a conda package with this environment variable pointing to the offline data (see conda-forge/geometric_features-feedstock#9). I used this package to run setup_ocean_region_groups.py from examples but without pointing to ./geometric_data. I ran this script in its own directory to make sure it wasn't picking up local geometric data. Everything ran as expected.