refactor(json): make jsonite optional with build tags (#1026)

* refactor(json): Restore gin support for app engine

Create new folder to support multiple json package.
restore gin support for app engine (disable jsonite through tags)

use jsoniter

$ go build -tags=jsoniter .

use default json

$ go build .

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* rename json file.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

* docs(json): add build tags document.

* fix(docs): markdown format.

* fix(json): missing space.

binding/json.go

@@ -7,11 +7,10 @@ package binding
 import (
 	"net/http"
 
-	"github.com/json-iterator/go"
+	"github.com/gin-gonic/gin/json"
 )
 
 var (
-	json                   = jsoniter.ConfigCompatibleWithStandardLibrary
 	EnableDecoderUseNumber = false
 )