Better docs and numerical stability

[gdalle]

No description provided.

[codecov]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (31de15c) 92.19% compared to head (d601615) 92.87%.

❗ Current head d601615 differs from pull request most recent head e92f1a3. Consider uploading reports for the commit e92f1a3 to get more accurate results

Files	Patch %	Lines
src/types/hmm.jl	50.00%	2 Missing ⚠️
src/utils/lightdiagnormal.jl	90.90%	2 Missing ⚠️
src/utils/valid.jl	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
+ Coverage   92.19%   92.87%   +0.67%     
==========================================
  Files          18       18              
  Lines         474      449      -25     
==========================================
- Hits          437      417      -20     
+ Misses         37       32       -5     

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