Soiling algorithm updates

[martin-springer]

• Code changes are covered by tests
• Code changes have been evaluated for compatibility/integration with TrendAnalysis
• New functions added to __init__.py
• API.rst is up to date, along with other sphinx docs pages
• Example notebooks are rerun and differences in results scrutinized
• Updated changelog

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.03%. Comparing base (b3927da) to head (5ded716).

Additional details and impacted files

@@               Coverage Diff               @@
##           development     #435      +/-   ##
===============================================
- Coverage        96.19%   96.03%   -0.17%     
===============================================
  Files               11       11              
  Lines             2209     2370     +161     
===============================================
+ Hits              2125     2276     +151     
- Misses              84       94      +10     

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[martin-springer]

Seems like the pytest.PytestRemovedIn8Warning: in the degradation_and_soiling_example notebook might be related to nbval < 0.10 computationalmodelling/nbval#180

However, nbval greater than 0.9.6 has a bug with semicolon computationalmodelling/nbval#194

@mdeceglie - I believe you removed most of the semicolons from the notebooks? If so, we could try using a newer version of nbval.

[mdeceglie]

There are still a few semicolons, I'm fine with attempting to remove them and updating nbval