update add_history_item doc, restructure reference

[sigma67]

closes #703

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.08%. Comparing base (338d63c) to head (c4cf089).
Report is 1 commits behind head on main.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #704   +/-   ##
=======================================
  Coverage   95.08%   95.08%           
=======================================
  Files          40       40           
  Lines        2361     2362    +1     
=======================================
+ Hits         2245     2246    +1     
  Misses        116      116           

Flag	Coverage Δ
unittests	95.08% <100.00%> (+<0.01%)	⬆️

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