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/http_fetch.go

@@ -0,0 +1,23 @@
+// httpfetch.go
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"io/ioutil"
+	"log"
+)
+
+func main() {
+	res, err := http.Get("http://www.google.com")
+	CheckError(err)
+	data, err := ioutil.ReadAll(res.Body)
+	CheckError(err)
+	fmt.Printf("Got: %q", string(data))
+}
+
+func CheckError(err error) {
+	if err != nil {
+		log.Fatalf("Get: %v", err)
+	}
+}