net/mail: add example to package

Change-Id: I912cafc66463f81cde839afc8f06b7eadcbf6f57
Reviewed-on: https://go-review.googlesource.com/11992Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/mail/example_test.go

+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package mail_test
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/mail"
+	"strings"
+)
+
+func ExampleParseAddressList() {
+	const list = "Alice <alice@example.com>, Bob <bob@example.com>, Eve <eve@example.com>"
+	emails, err := mail.ParseAddressList(list)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	for _, v := range emails {
+		fmt.Println(v.Name, v.Address)
+	}
+
+	// Output:
+	// Alice alice@example.com
+	// Bob bob@example.com
+	// Eve eve@example.com
+}
+
+func ExampleParseAddress() {
+	e, err := mail.ParseAddress("Alice <alice@example.com>")
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println(e.Name, e.Address)
+
+	// Output:
+	// Alice alice@example.com
+}
+
+func ExampleReadMessage() {
+	msg := `Date: Mon, 23 Jun 2015 11:40:36 -0400
+From: Gopher <from@example.com>
+To: Another Gopher <to@example.com>
+Subject: Gophers at Gophercon
+
+Message body
+`
+
+	r := strings.NewReader(msg)
+	m, err := mail.ReadMessage(r)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	header := m.Header
+	fmt.Println("Date:", header.Get("Date"))
+	fmt.Println("From:", header.Get("From"))
+	fmt.Println("To:", header.Get("To"))
+	fmt.Println("Subject:", header.Get("Subject"))
+
+	body, err := ioutil.ReadAll(m.Body)
+	if err != nil {
+		log.Fatal(err)
+	}
+	fmt.Printf("%s", body)
+
+	// Output:
+	// Date: Mon, 23 Jun 2015 11:40:36 -0400
+	// From: Gopher <from@example.com>
+	// To: Another Gopher <to@example.com>
+	// Subject: Gophers at Gophercon
+	// Message body
+}