Add contributor roles

[cthoyt]

Closes #73. Supercedes #75

This PR enables annotating author roles using the Contribution Role Taxonomy (CRediT). It also enables (optionally) annotating the contribution degree, as suggested by JATS.

It does the following:

• [x] Add contribution list to end of default.latex (after reference list)
• [x] Add contribution list to end of preprint.latex (after reference list)
• [x] JATS support
  • [x] Implementation and testing
  • [x] Wait for a 3.6.3 release of Pandoc containing https://github.com/jgm/pandoc/pull/10153, which does the heavy lifting

Blockers

• [ ] #100

Demo

Here's what this looks like at the end of the main PDF build:

Future Work

Future work for future PRs:

1. Work with Crossref to get a reasonable model for capturing this. Crossref is currently discussing supporting this.

2. See how this fits in the ConTeXt template, if this gets picked up by Open Journals