Cleanup of units and constants.
Cleanup units and physical constants (with refactoring). Added more examples.
Fix error in doc.
 Minor changes in abinitio objects.
Merge remote-tracking branch 'mpmaster/master'
 Modified HighSymmKpath: use true division everywhere in the module + dump UserWarnings
 if the lattice_type and/or the spacegroup_symbol returned by spglib do not have the expected format.
 spglib: Fix the undefined behaviour due to overlapping strings in the call to sprintf.
 New objects needed for the submission of AbinitTasks.