Make the program easier to use locally

[tarleb]

Some users do not want to install or use Docker. We currently provide a Makefile, but it sometimes goes out of sync with the containerized version and might not work as well on Windows.

Ideally, Inara should be a single downloadable zip-archive or even a single script with minimal dependencies.

A good way to achieve this would be to refactor it into a single Lua program that can be run with pandoc-lua. This would eliminate the need for an additional entrypoint.sh script, could help to avoid certain complexities in the configuration, and allow for more flexible output generation.

The last point is of particularly importance for the production of Pubmed compliant artifacts.

Possible risks with that approach:

• Pandoc might not expose all required features via its Lua API.
• Configuration methods might have to be modified.

[tarleb]

Experimental code for that idea: #61.