Add handling of multi-line (i.e. cell) key-value
Add handling of multi-line (i.e. cell) key-value

Addresses MRtrix3/mrtrix3#2386
MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3