Schema exceptions refactor

[p1c2u]

Fixes #160

[codecov]

Codecov Report

Merging #168 into master will increase coverage by 0.13%.
The diff coverage is 83.33%.

@@            Coverage Diff             @@
##           master     #168      +/-   ##
==========================================
+ Coverage    96.4%   96.54%   +0.13%     
==========================================
  Files          67       67              
  Lines        1698     1706       +8     
==========================================
+ Hits         1637     1647      +10     
+ Misses         61       59       -2

Impacted Files	Coverage Δ
openapi_core/schema/schemas/unmarshallers.py	100% <100%> (ø)	⬆️
openapi_core/schema/parameters/exceptions.py	85.18% <100%> (+1.18%)	⬆️
openapi_core/validation/response/validators.py	100% <100%> (ø)	⬆️
openapi_core/schema/media_types/models.py	90.24% <62.5%> (-4.36%)	⬇️
openapi_core/schema/schemas/exceptions.py	84.31% <72.41%> (+0.64%)	⬆️
openapi_core/schema/parameters/models.py	97.26% <75%> (ø)	⬆️
openapi_core/validation/request/validators.py	95.06% <90%> (+0.46%)	⬆️
openapi_core/schema/schemas/models.py	95.3% <91.66%> (+0.68%)	⬆️
openapi_core/schema/schemas/_validators.py	92.5% <0%> (-2.5%)	⬇️
... and 1 more

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