Update CFFs once Zenodo DOIs have been minted for archived versions

[jbstatgen]

From citation.CFF:

identifiers:
  - type: "doi"
    value: "10.xxxxxx"
    description: "DOI for this repository archived in Zenodo"
repository-code: "https://github.com/tdwg/ltc"
url: "https://github.com/tdwg/ltc/wiki"

citation_release.CFF:

identifiers:
  - type: "doi"
    value: "10.xxxxxx"
    description: "DOI for this repository archived in Zenodo"
repository-code: "https://github.com/tdwg/ltc/"
url: "https://tdwg.github.io/ltc/"

The CFF standard allows the association of identifiers with the publication or published resource, e.g. a DOI.
We thought it sensible, once LtC is ratified to archive the release version and a current repository snapshot on Zenodo. This apparently will generate a DOI for each of them.
Once this is done, the CFFs should be updated with the DOIs (currently a placeholder is present).

Alternatively, the identifier keyword should be removed from the CFFs.

[magpiedin]

@jbstatgen -- We'll follow up on this (happy to help!) at the July monthly LtC call, after the term IRI & versioning is worked out - #85 (& related issues)

[magpiedin]

mini-update:

• whenever the LtC maintenance group needs to update its author list, we will update the CFF
• @ben-norton is updating stadocgen to pull from that / generate the authors YAML file from CFF