ENH: add dtype parameter to reciprocal_space and use correct dtype in pre- and postprocess
ENH: add dtype parameter to reciprocal_space and use correct dtype in pre- and postprocess

Additional changes:
- better dtype printing
- improved docs

odlgroup/odl,aringh/odl,aringh/odl,odlgroup/odl,kohr-h/odl,kohr-h/odl