First implementation of docs

[aknierim]

• Add a first (simple) implementation of docs for pyvisgen
• This is still WIP, some fixes are necessary for the automodapi summary generation of pyvisgen.layouts and pyvisgen.gridding

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.93%. Comparing base (37a740c) to head (37801d0).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #47      +/-   ##
==========================================
- Coverage   87.93%   85.93%   -2.01%     
==========================================
  Files          13       19       +6     
  Lines         920      974      +54     
==========================================
+ Hits          809      837      +28     
- Misses        111      137      +26     

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