As the first step of easing and generalizing access to Gemini3D from other libraries and programs, make a C CLI to complement the Fortran CLI. It's possible that the Fortran CLI will go away to be replaced by C CLI. From user's perspective little would change.

More FindHDF5 fixes based on user experiences

More MSIS 2.0 fixes--require /msis_version in HDF5 input instead of CLI argument for MSIS version. The CLI seemed to give intermittent all-zero output from MSIS 2.0. Added more MSIS 2.0 unit tests

Add requirements.json that's human readable. Using cmake -P scripts/requirements.cmake will print how to install the requirements on the user's particular computer.