Improvements to bidict view methods and docs.

[jab]

Also

• rename tests/properties -> tests/property_tests
• work around issue with upgrading to latest setuptools ([BUG] latest setuptools release (60.3.0) broke pip? pypa/setuptools#3002)

[gitpod-io]

[codecov]

Codecov Report

Merging #229 (5ac7358) into main (69b83ff) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #229   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           16        15    -1     
  Lines          607       604    -3     
  Branches        87        88    +1     
=========================================
- Hits           607       604    -3     

Impacted Files	Coverage Δ
bidict/_abc.py	100.00% <ø> (ø)
bidict/_base.py	100.00% <100.00%> (ø)
bidict/_bidict.py	100.00% <100.00%> (ø)
bidict/_frozenbidict.py	100.00% <100.00%> (ø)
bidict/_orderedbase.py	100.00% <100.00%> (ø)

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