[RELEASE ISSUE] Checklist before releasing next version of powder dictionary

[jamesrhester]

Modelled on the one used for core CIF. Any volunteers for release manager (someone to keep things ticking over). This version will be the reference for Volume G 2nd Edition.

• Release manager appointed
• _dictionary_audit.revision comments summarised
• Release branch created
• Next version placeholder created in dictionary_audit section in master branch
• Plain text summary of changes created (ideally automatic Github changeset comments)
• cif_core, pddmg mailing list advised
• Rietveld mailing list advised
• All comments/issues arising during review period addressed (add to list below)
• Final DOI and URL edited into file (IUCr Chester office to advise of DOI)
• Github release tagged
• Zenodo/IUCr updated with released file

Outstanding pull requests/ issues added below: