Tests added, one bug fixed, and some documentation

[maxeruth]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 77.27273% with 5 lines in your changes missing coverage. Please review.

Project coverage is 48.10%. Comparing base (a3d60e3) to head (275a141).
Report is 30 commits behind head on main.

Files with missing lines	Patch %	Lines
src/Birkhoff/BirkhoffAveraging.jl	77.27%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #50      +/-   ##
==========================================
- Coverage   49.73%   48.10%   -1.63%     
==========================================
  Files          21       22       +1     
  Lines        2075     2644     +569     
==========================================
+ Hits         1032     1272     +240     
- Misses       1043     1372     +329     

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