* support bind http header param #1956
update #1956
```
package main
import (
"fmt"
"github.com/gin-gonic/gin"
)
type testHeader struct {
Rate int `header:"Rate"`
Domain string `header:"Domain"`
}
func main() {
r := gin.Default()
r.GET("/", func(c *gin.Context) {
h := testHeader{}
if err := c.ShouldBindHeader(&h); err != nil {
c.JSON(200, err)
}
fmt.Printf("%#v\n", h)
c.JSON(200, gin.H{"Rate": h.Rate, "Domain": h.Domain})
})
r.Run()
// client
// curl -H "rate:300" -H "domain:music" 127.0.0.1:8080/
// output
// {"Domain":"music","Rate":300}
}
```
* add unit test
* Modify the code to get the http header
When the http header is obtained in the standard library,
the key value will be modified by the CanonicalMIMEHeaderKey function,
and finally the value of the http header will be obtained from the map.
As follows.
```go
func (h MIMEHeader) Get(key string) string {
// ...
v := h[CanonicalMIMEHeaderKey(key)]
// ...
}
```
This pr also follows this modification
* Thanks to vkd for suggestions, modifying code
* Increase test coverage
env GOPATH=`pwd` go test github.com/gin-gonic/gin/binding -coverprofile=cover.prof
ok github.com/gin-gonic/gin/binding 0.015s coverage: 100.0% of statements
* Rollback check code
* add use case to README.md
