Add Fortran/C Bindings

[wavefunction91]

This is a requirement for integration with legacy codes.

[awvwgk]

Providing C bindings in GauXC would be a great start. For Fortran bindings there are now several options, we can define those entirely in C using ISO_Fortran_binding.h or in Fortran via iso_c_binding. Maybe we can give the Fortran binding from C a chance as it allows to preserve most of the shape information from the Fortran side.