Unpin numpy version; require python>=3.8
Created by: emthompson-usgs
- The issue with numpy and obspy is now fixed and so we should be able to unpin the numpy version and hopefully this will help the install solve for dependencies.
- Restricting to python >=3.8 which is the oldest version we run with the CI systems.
- Git ignore C files built by cython and delete them from the repo.