Improve documentation for the C API
Improve documentation for the C API

chemfiles/chemfiles,lscalfi/chemfiles,lscalfi/chemfiles,chemfiles/chemfiles,lscalfi/chemfiles,Luthaf/Chemharp,chemfiles/chemfiles,Luthaf/Chemharp,Luthaf/Chemharp,chemfiles/chemfiles,lscalfi/chemfiles