Generate DOI numbers for each release

[donkirkby]

The Zenodo project makes it easy to generate DOI numbers for each GitHub release, and DOI numbers make it easy for researchers to cite a specific version of MiCall.

• configure Zenodo to generate the DOI numbers
• add current DOI number to BaseSpace description
• add some DOI information to small print on resistance reports (may have problems updating the DOI before tagging the release, but look at the feature for reserving a DOI)
• add current DOI number to project README
• update release instructions to include DOI updates to the items listed above