resolve #368 add option to UseNumber() in gin.Context.BindJSON()

[whirosan]

resolve #368
I added an option EnableJsonDecoderUseNumber, so that you can choose whether or not to enable UseNumber in the JSON decoder.
Please review.

[codecov]

Codecov Report

Merging #997 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #997      +/-   ##
==========================================
+ Coverage   96.52%   96.53%   +<.01%     
==========================================
  Files          16       16              
  Lines        1412     1414       +2     
==========================================
+ Hits         1363     1365       +2     
  Misses         39       39              
  Partials       10       10

Impacted Files	Coverage Δ
mode.go	82.6% <100%> (+1.65%)	⬆️

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[thinkerou]

Sorry I don't understand the pr to solve what?

If I have the follow code:

type Login struct {
    User     string `form:"user" json:"user" binding:"required"`
    Password int    `form:"password" json:"password" binding:"required"`
}

......

var j Login
err := c.BindJSON(&j)

If I don't use gin.EnableJsonDecoderUseNumber(), it is also OK.