Zenodo upload infrastructure

adds infrastructure for:
- bumping versions in CITATION.cff and .zenodo.json from release tag in GitHub release UI
- getting provisional DOI from Zenodo sandbox
- updating the DOI in CITATION.cff
- uploading to the Zenodo sandbox
- retagging the version to include the changes that were uploaded
makes sure all builds and releases, and PyPI releases are now:
- downstream of the above so they include all the committed changes
- enable skipping of the retagging on non-Zenodo release

alexlancaster / pypop