Add template tags to automatically insert GitHub versions, Zenodo citations, & list of contributors

[wragge]

I've already coded these, it's just a matter of inserting the tags into all the index pages. The GH version tag goes at the top, the contributors and Zenodo tags at the bottom.

For the Zenodo tag to work #22 has to be done.

Tags are:

• {{ git_latest_tag() }}
• {{ repo_contributors() }}
• {{ zenodo_citation() }}