add missing code example of chapter 15.3 (#678)

example code from:
https://sites.google.com/site/thewaytogo2012/Downhome/Topic3/code_examples.zip

eBook/examples/chapter_15/twitter_status.go

@@ -0,0 +1,42 @@
+// twitter_status.go
+package main
+
+import (
+	"net/http"
+	"fmt"
+	"encoding/xml"
+	"io/ioutil"
+)
+/* these structs will house the unmarshalled response. 
+   they should be hierarchically shaped like the XML 
+   but can omit irrelevant data. */
+type Status struct {
+	Text string
+}
+
+type User struct {
+	XMLName xml.Name
+	Status  Status
+}
+// var user User
+
+func main() {
+	// perform an HTTP request for the twitter status of user: Googland  
+	resp, _ := http.Get("http://twitter.com/users/Googland.xml")
+	// initialize the structure of the XML response  
+	user := User{xml.Name{"", "user"}, Status{""}}
+	// unmarshal the XML into our structures 
+	defer resp.Body.Close()
+	if body, err := ioutil.ReadAll(resp.Body); err != nil {
+			fmt.Printf("error: %s", err.Error())
+	} else {
+			fmt.Printf("%s ---", body)
+			xml.Unmarshal(body, &user)
+	}
+	fmt.Printf("name: %s ", user.XMLName)
+	fmt.Printf("status: %s", user.Status.Text)
+}
+/* Output:
+status: Robot cars invade California, on orders from Google: Google has been testing self-driving cars ... http://bit.ly/cbtpUN http://retwt.me/97p<exit code="0" msg="process exited normally"/>
+After Go1: no output: name: { user} status:
+*/