Add error as a Primitive Type

[Niennienzz]

Describe the PR

• When the handler is returning a custom error struct type, and it contains the built-in error interface like below, the error :cannot find type definition: error would occur.

type ErrorResponse struct {
	Message string `json:"message"`
	Cause   error  `json:"cause"`
}

• I am thinking, since the error interface is also a built-in type, and when it marshals to JSON using the interface (instead of any underneath implementation), it should be translated to a string.
• Please let me know if/where I should add more tests!

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Relation Issue

#1171

[ubogdan]

@Niennienzz Thanks for your contribution, but we won't make this kind of change because the error type is an interface and doesn't get marshaled by default.
We may add the feature to skip this field with a warning so "swag" will not end with an error, but this is entirely another story.

[codecov]

Codecov Report

Merging #1188 (370d098) into master (636f456) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1188   +/-   ##
=======================================
  Coverage   95.03%   95.03%           
=======================================
  Files          10       10           
  Lines        2557     2557           
=======================================
  Hits         2430     2430           
  Misses         69       69           
  Partials       58       58           

Impacted Files	Coverage Δ
schema.go	100.00% <100.00%> (ø)

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[ubogdan]

Please let me know if you are interested on making the change described by me or we can close this PR.

[Niennienzz]

Please let me know if you are interested on making the change described by me or we can close this PR.

Please close for now. I would love to, but currently I am a bit busy with other projects...