fix x-logo vendor extension & parse x-codeSamples from files

[Nerzal]

Describe the PR

1. the x-logo vendor extension must reside inside the info element. Fixes x-logo is broken #763
2. I added the possibility to parse x-codeSamples from files similar to the markdown feature. This removes optical waste from the actual code by moving it into separate files.
3. Fixes x-tagGroups is broken #781

Relation issue
none

Additional context

1. To fix the x-logo vendor extension I just used the existing vendor extension parsing logic to achieve that.
2. NewOperation does now also take functional options. This was needed to hand the path parameter to the Operation
3. This pr should fix even more vendor extensions beside the x-tagGroups is broken #781 issue, cause there is a bug in the underlying spec library, which always called toLower() on the attributes which generates wrong tags in the documentation

[codecov]

Codecov Report

Merging #760 into master will increase coverage by 1.41%.
The diff coverage is 81.25%.

@@            Coverage Diff             @@
##           master     #760      +/-   ##
==========================================
+ Coverage   80.91%   82.33%   +1.41%     
==========================================
  Files           8        8              
  Lines        1588     1608      +20     
==========================================
+ Hits         1285     1324      +39     
+ Misses        187      168      -19     
  Partials      116      116              

Impacted Files	Coverage Δ
schema.go	84.50% <ø> (ø)
parser.go	78.60% <80.00%> (+2.88%)	⬆️
operation.go	87.10% <80.55%> (-0.55%)	⬇️
gen/gen.go	95.27% <100.00%> (+0.03%)	⬆️

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[Nerzal]

@easonlin404 @sdghchj @pei0804 could one of you please review? :)
We could need this for several projects in my company 👍

[Nerzal]

build is green now :)

[Nerzal]

@easonlin404 could u please review?

[sdghchj]

Sorry, I haven't see anywhere SetCodeExampleFilesDirectory is called, that is, codeExampleFilesDir in an operation object has not been initialized

[Nerzal]

is the build pipeline broken?

[Nerzal]

This PR does now fix all vendor extensions, which contain an uppercase letter.
And all comments have been fixed.

@easonlin404 @pei0804 @sdghchj could anyone of you please review again?

[WelverinRaven]

I'd like to use this feature too.

[easonlin404]

https://travis-ci.org/github/swaggo/swag/jobs/722247122 The CI still builds failed. @Nerzal could you kindly take a look?

[Nerzal]

done

[Nerzal]

The reporting of the status seems to be broken in ci, but the build is green ->
https://travis-ci.org/github/swaggo/swag/builds/722323442

[Nerzal]

@easonlin404 could you please have a look again? :)

[Nerzal]

So the CI is broken, which is unrelated to that PR.
It feels like noone is actively maintaining this repo anymore :(

[kplachkov]

why this merge is taking so long?

[kplachkov]

@Nerzal when you are available, can you resolve the merge conflicts?

[Nerzal]

@kplachkov done

[Nerzal]

Well reporting from travis-ci still seems to be broken.

Build is successful:

[kplachkov]

okay, if everything is green lets merge this PR @easonlin404

[easonlin404]

LGTM