Updated API

[glevv]

• Added Staudte kurtosis;
• Added IER;
• Fixed bug in Crow & Siddiqui kurtosis;
• Fixed bug in associations;
• Updated API for associations;
• Updated tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (280d24b) to head (b4efff9).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #115   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           12        12           
  Lines          431       466   +35     
=========================================
+ Hits           431       466   +35     

Flag	Coverage Δ
smart-tests	100.00% <100.00%> (ø)

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