Annotate and document anchor.py

[knutnergaard]

No description provided.

[knutnergaard]

@benkiel With these latest PRs, the work to improve object documentation and add type annotation should be done, barring any errors or necessary changes, in which case, please let me know.

[codecov]

Codecov Report

Attention: Patch coverage is 91.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 76.50%. Comparing base (653c3d7) to head (199823e).
Report is 1 commits behind head on v1.

Files with missing lines	Patch %	Lines
Lib/fontParts/base/anchor.py	91.66%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##               v1     #817      +/-   ##
==========================================
- Coverage   76.56%   76.50%   -0.07%     
==========================================
  Files          42       42              
  Lines        6452     6461       +9     
  Branches      963      966       +3     
==========================================
+ Hits         4940     4943       +3     
- Misses       1274     1278       +4     
- Partials      238      240       +2     

Files with missing lines	Coverage Δ
Lib/fontParts/base/anchor.py	91.52% <91.66%> (-2.97%)	⬇️

... and 1 file with indirect coverage changes

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