Package version definitions

[jessjaco]

This may belong more in dep-tools repo, but since the coastlines are in more active development, it's here.

dep-tools has "*" for versions in pyproject.toml because versions may differ between local and planetary computer installations. But this is not ideal.

Of particular issue is that the version of gdal must match local install

[jessjaco]

For now I'm leaving gdal version undefined in requirements.txt (be careful when running pip-compile) and including a local constraints.txt file.