code: func (c *C) String(status int, format string, val ...interface{}) {
  	c.Writer.Header().Set(contentType, "text/html; charset=UTF-8")
  	c.Writer.WriteHeader(status)
  
  	buf := bufPool.Get()
  	defer bufPool.Put(buf)
  
  	if len(val) == 0 {
  		buf.WriteString(format)
  	} else {
  		buf.WriteString(fmt.Sprintf(format, val...))
  	}
  
  	c.Writer.Write(buf.Bytes())
  }
docs: //String response with text/html; charset=UTF-8 Content type