Better handling of pre-existing sources, better error messages

• No longer looks up bibliographic data for sources that are defined in the references metadata field or in a bibliography file.
• Now prints an error message, rather than a stack trace, when a source is not found in Zotero.
• Minor changes to documentation.

Better error handling

Some people have been using this script for a while now -- without major hiccups. So I guess it's time for v1.0.0.

Improvements

• If you're using Pandoc v2.10 or newer, errors no longer abort
  document compilation and error messages are more to the point.
• Error messages are formatted more nicely.

Bugfixes

• The test suite can now test under 'real world' conditions again.
• warn no longers throws an error if it's called with arguments to msg.
• add_references creates a empty array instead of an empty object for references.

Varia

• Minor improvements to documentation.
• Data files of the test suite no longer get updated by testing.

Minor corrections

• write_json_file now uses the operating sytem's end of line sequence.
• Adapted test suite to now grouping behaviour of the citation processor.
• Simplified some functions.
• Moved code for testing into its own script.
• Several minor corrections and improvements to the documentation.

Support for Pandoc v2.11

Issues addressed

Using formatted fields only worked because of an unintended behaviour in how pandoc-citeproc handles the references metadata field. However, starting with Pandoc v2.11, Pandoc no longer uses pandoc-citeproc, but processes citations itself. And it handles references metadata field correctly (see issue #6722 of Pandoc for details). This release addresses this. Thanks to @njbart for catching it early!

Documentation

• Updated to reflect Pandoc v2.11.
• Many typos corrected.
• Other minor improvements.

Varia

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

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.

Minor update

httpd now makes sure only to return when it accepts requests. This makes the test suite more robust.

Minor update

The test suite is now more robust and no longer needs Zotoro, zotxt, or Better BibTeX. It does need Python now though.

Minor update

• More robust error handling.
• Minor performance improvements.

Minor fix

The manpage contained en-dashes (“–”) instead of double hyphens (“--”). Fixed.

Bugfix

File I/O errors could have been reported incorrectly. Fixed.