Add _space_group.reference_setting _space_group.transform_Pp_abc _space_group.transform_Qq_xyz

[rowlesmr]

From COMCIFS/cif_mag#75 (comment)

Added

• _space_group.reference_setting
• _space_group.transform_Pp_abc
• _space_group.transform_Qq_xyz

with text taken from from https://www.iucr.org/__data/iucr/cif/dictionaries/cif_sym_1.0.1.dic

Updated first URL in second reference in _space_group.reference_setting

Probably need to update ITA reference in _space_group.reference_setting, but I don't have access to latest copy.

I took an educated guess at the _type.* values.

Should the enumeration go into templ_enum.cif?

[vaitkus]

Thank you for taking on the PR. I just discovered that there is a draft version of the DDLm symCIF dictionary that might prove useful (see https://github.com/COMCIFS/comcifs.github.io/blob/main/draft/cif_sym.dic).

[rowlesmr]

That is helpful!

[rowlesmr]

Differences from https://github.com/COMCIFS/comcifs.github.io/blob/main/draft/cif_sym.dic

This PR:

• _type.contents Text for reference_setting. The enumerations are described as '_space_group.IT_number:_space_group.name_Hall'. The _type.contents of _space_group.name_hall is Text
• _type.purpose Encode for transform_*, mirroring that of the symops, as information is encoded in a machine-readable manner in the value.
• AFAIK the _description_example.case/detail are in the correct order