Testing changes for Pandoc v2.11

Bugs fixed

Using formatted fields only worked because of a bug in how pandoc-citeproc
handles the references metadata field. pandoc-citeproc is no longer
needed starting with Pandoc v2.11, which also treats the references
metadata field correctly. This should have been fixed.

Documentation

• Updated to reflect new invocation of the citation processor in Pandoc v2.11.
• Many typos corrected.
• Other minor improvements.

Varia

• Test suite no longer requires Python.
• Updated lunajson to v1.2.3-1.