Fixed navigation oddities with single page docs

[josephlewis42]

Fixes #16. Changes the logic for expanding sections to ignore the special case of the index. Example showing Lua now works:

I additionally validated RequireJS which has much of its content in the index but other parts in different pages, it behaves as expected.

A longer term, better fix for this is #24.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.61%. Comparing base (2e61d1f) to head (ffb63ca).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #25      +/-   ##
==========================================
+ Coverage   92.56%   92.61%   +0.04%     
==========================================
  Files           4        4              
  Lines         323      325       +2     
  Branches       43       44       +1     
==========================================
+ Hits          299      301       +2     
  Misses         22       22              
  Partials        2        2              

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[benoit74]

LGTM