Better error handling when fetching documents

[dbanty]

closes #128

[codecov]

Codecov Report

Merging #132 into main will increase coverage by 0.08%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             main      #132      +/-   ##
===========================================
+ Coverage   99.91%   100.00%   +0.08%     
===========================================
  Files          40        40              
  Lines        1124      1158      +34     
===========================================
+ Hits         1123      1158      +35     
+ Misses          1         0       -1     

Impacted Files	Coverage Δ
openapi_python_client/__init__.py	100.00% <100.00%> (+0.67%)	⬆️
openapi_python_client/parser/errors.py	100.00% <0.00%> (ø)
openapi_python_client/parser/openapi.py	100.00% <0.00%> (ø)
openapi_python_client/parser/reference.py	100.00% <0.00%> (ø)
openapi_python_client/parser/responses.py	100.00% <0.00%> (ø)
openapi_python_client/parser/properties.py	100.00% <0.00%> (ø)

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