Add support for YAML documents

[dbanty]

Closes #111

[codecov]

Codecov Report

Merging #127 into main will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #127   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           40        40           
  Lines         1140      1139    -1     
=========================================
- Hits          1140      1139    -1     

Impacted Files	Coverage Δ
openapi_python_client/__init__.py	100.00% <100.00%> (ø)

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