Add anyOf

[sisp]

This is a continuation of #288 (thanks to @allcaps for your work).

I've addressed @p1c2u's comments in #288 and updated the branch to the latest state of master. Any feedback is most welcome. :slightly_smiling_face:

[codecov[bot]]

Codecov Report

Merging #354 (c6dd04b) into master (bf2f13d) will decrease coverage by 0.81%. The diff coverage is 92.85%.

:exclamation: Current head c6dd04b differs from pull request most recent head 2b05067. Consider uploading reports for the commit 2b05067 to get more accurate results

@@            Coverage Diff             @@
##           master     #354      +/-   ##
==========================================
- Coverage   96.72%   95.91%   -0.82%     
==========================================
  Files          80       80              
  Lines        1743     1714      -29     
==========================================
- Hits         1686     1644      -42     
- Misses         57       70      +13     

Impacted Files	Coverage Δ
openapi_core/schema/schemas.py	100.00% <ø> (ø)
...penapi_core/unmarshalling/schemas/unmarshallers.py	92.89% <92.85%> (-0.86%)	:arrow_down:
openapi_core/contrib/falcon/responses.py	92.30% <0.00%> (-7.70%)	:arrow_down:
openapi_core/contrib/django/__init__.py	100.00% <0.00%> (ø)
openapi_core/contrib/django/requests.py	100.00% <0.00%> (ø)
openapi_core/contrib/falcon/handlers.py	100.00% <0.00%> (ø)
openapi_core/contrib/django/responses.py	100.00% <0.00%> (ø)
openapi_core/contrib/falcon/middlewares.py	100.00% <0.00%> (ø)
openapi_core/contrib/django/middlewares.py
openapi_core/contrib/django/handlers.py
... and 4 more

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[sisp]

@p1c2u Could you please review this PR? Do you insist on covering the two currently uncovered sections? The equivalent sections for unmarshaling oneOf in ObjectUnmarshaller::_unmarshal_object are not covered either at the moment.

[sisp]

@p1c2u Tests are passing now. Would you mind doing a review?

[p1c2u]

Closing in favor of #423 Thank you all for your contribution.