Reduce code complexity

[ubogdan]

Describe the PR
code-refactoring

$ ~/go/bin/gocyclo -over 15 .
48 swag (*Parser).parseField parser.go:1010:1
46 swag (*Parser).ParseGeneralAPIInfo parser.go:177:1
33 swag (*Parser).parseStructField parser.go:764:1
16 swag (*Operation).parseAndExtractionParamAttribute operation.go:233:1

Relation issue
None

Additional context
Original results

Gocyclo calculates cyclomatic complexities of functions in Go source code. The cyclomatic complexity of a function is calculated according to the following rules: 1 is the base complexity of a function +1 for each 'if', 'for', 'case', '&&' or '||' Go Report Card warns on functions with cyclomatic complexity > 15.

swag/parser.go
Line 177: warning: cyclomatic complexity 83 of function (*Parser).ParseGeneralAPIInfo() is high (> 15) (gocyclo)
Line 1081: warning: cyclomatic complexity 48 of function (*Parser).parseField() is high (> 15) (gocyclo)
Line 834: warning: cyclomatic complexity 23 of function (*Parser).parseStruct() is high (> 15) (gocyclo)
Line 694: warning: cyclomatic complexity 22 of function (*Parser).parseTypeExpr() is high (> 15) (gocyclo)
Line 1017: warning: cyclomatic complexity 17 of function (*Parser).parseAnonymousField() is high (> 15) (gocyclo)
swag/operation.go
Line 241: warning: cyclomatic complexity 29 of function (*Operation).parseAndExtractionParamAttribute() is high (> 15) (gocyclo)
Line 60: warning: cyclomatic complexity 27 of function (*Operation).ParseComment() is high (> 15) (gocyclo)

[codecov-io]

Codecov Report

Merging #487 into master will increase coverage by 1.12%.
The diff coverage is 84.74%.

@@            Coverage Diff            @@
##           master    #487      +/-   ##
=========================================
+ Coverage   86.58%   87.7%   +1.12%     
=========================================
  Files           7       7              
  Lines        1558    1489      -69     
=========================================
- Hits         1349    1306      -43     
+ Misses        120     104      -16     
+ Partials       89      79      -10

Impacted Files	Coverage Δ
operation.go	95.45% <100%> (+0.36%)	⬆️
parser.go	82.59% <81.17%> (+1.52%)	⬆️

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[easonlin404]

LGTM