suport global options

[zwczou]

package main

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

	"github.com/zwczou/grequests"
)

func main() {
	sess := grequests.NewSession(&grequests.RequestOptions{
		Headers: map[string]string{
			"Accept": "*/*",
		},
		UserAgent: "client/1.0",
	})

	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))
}```

[levigross]

@zwczou Thank you very much 😄 I do have a non-descriptive task to clean sessions up (#34) but this is a great start!