add global options

[zwczou]

package main

import (
	"log"
	"net/http/httputil"

	"github.com/levigross/grequests"
)

func main() {
	sess := grequests.NewSession(&grequests.RequestOptions{
		Headers: map[string]string{
			"Accept":          "*/*",
		},
		UserAgent: "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/54.0.2840.59 Safari/537.36",
	})
	sess = grequests.NewSession(nil)

	resp, err := sess.Get("http://baidu.com", nil)
	if err != nil {
		log.Fatal(err)
	}
	body, err := httputil.DumpRequest(resp.RawResponse.Request, true)
	if err != nil {
		log.Fatal(err)
	}
	println(string(body))
}