Add InputModel OperationOption

[FabienM]

InputModel overrides the binding model of an operation, allowing usage of generic handlers.

type testInputModel struct {
    PathParam1 string `path:"a"`
    PathParam2 int    `path:"b"`
    QueryParam string `query:"q"`
}

fizz.GET("/test/:a/:b", []OperationOption{
        ID("GetTest2"),
        InputModel(&testInputModel{}),
    },
    tonic.Handler(func(c *gin.Context) error {
        return nil
    }, 200)
)

[codecov[bot]]

Codecov Report

Merging #18 into master will increase coverage by 0.02%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #18      +/-   ##
==========================================
+ Coverage   96.97%   96.99%   +0.02%     
==========================================
  Files           7        7              
  Lines         860      866       +6     
==========================================
+ Hits          834      840       +6     
  Misses         14       14              
  Partials       12       12

Impacted Files	Coverage Δ
fizz.go	100% <100%> (ø)	:arrow_up:

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