joss paper draft

[janfb]

• add paper draft
• add action to test-build from markdown.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.36%. Comparing base (428fc93) to head (1770e12).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1294       +/-   ##
===========================================
- Coverage   89.30%   78.36%   -10.94%     
===========================================
  Files         119      119               
  Lines        8721     8728        +7     
===========================================
- Hits         7788     6840      -948     
- Misses        933     1888      +955     

Flag	Coverage Δ
unittests	78.36% <ø> (-10.94%)	⬇️

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see 33 files with indirect coverage changes

[tomMoral]

a few comments and nitpicks.
This looks very nice! Thanks for putting this together.