Add additional meta data to schema and errors

[danielbradburn]

This pull request adds additional information in the schema object (name and dered) and additional stores a reference in schema errors to the schema that caused the error. This gives us the ability to provide additional context when an error occurs, for example if the schema is named then the name of the schema, or if the yaml is parsed with ruamel.yaml we can show the line and column number that generated the error.

[codecov[bot]]

Codecov Report

Merging #120 into master will increase coverage by 1.61%. The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #120      +/-   ##
=========================================
+ Coverage   96.19%   97.8%   +1.61%     
=========================================
  Files          54      54              
  Lines        1444    1457      +13     
=========================================
+ Hits         1389    1425      +36     
+ Misses         55      32      -23

Impacted Files	Coverage Δ
openapi_core/schema/schemas/generators.py	100% <100%> (ø)	:arrow_up:
openapi_core/schema/schemas/models.py	98.72% <100%> (+4.49%)	:arrow_up:
openapi_core/schema/schemas/registries.py	100% <100%> (ø)	:arrow_up:
openapi_core/schema/schemas/exceptions.py	100% <100%> (+17.3%)	:arrow_up:
openapi_core/schema/schemas/factories.py	100% <100%> (ø)	:arrow_up:

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