gin/binding
guonaihong 53df00ffe4 binding: add BindPlain function
```go
package main

import (
	"github.com/gin-gonic/gin"
)

func main() {
	router := gin.Default()
	router.POST("/", func(c *gin.Context) {
		var s string
		c.BindPlain(&s)
		c.String(200, s)
	})

	router.Run()
}

// client
// curl -d "test string" 127.0.0.1:8080
// output
// test string
```
2019-09-03 22:50:13 +08:00
..
2018-11-06 09:49:45 +08:00
2019-09-03 22:50:13 +08:00
2019-09-03 22:50:13 +08:00
2018-11-05 14:17:04 +08:00
2018-11-22 09:29:48 +08:00
2018-11-06 09:49:45 +08:00