strings: Add examples for HasPrefix and HasSuffix

These methods didn't had any examples, so added them. Examples makes things more clear
diff --git a/src/strings/example_test.go b/src/strings/example_test.go
index 7243e16..b7763bb 100644
--- a/src/strings/example_test.go
+++ b/src/strings/example_test.go
@@ -223,3 +223,19 @@ func ExampleTrimPrefix() {
 	fmt.Print("Hello" + s)
 	// Output: Hello, world!
 }
+
+func ExampleHasPrefix() {
+	fmt.Println(strings.HasPrefix("hello", "hell"))
+	fmt.Println(strings.HasPrefix("hello", "heaven"))
+	// Output:
+	// true
+	// false
+}
+
+func ExampleHasSuffix() {
+	fmt.Println(strings.HasSuffix("hello", "llo"))
+	fmt.Println(strings.HasSuffix("hello", "hell"))
+	// Output:
+	// true
+	// false
+}

Change-Id: I5d451c669bd05e19a2afc33ed2ec59b280c2c2d9
Reviewed-on: https://go-review.googlesource.com/12065
Reviewed-by: Russ Cox <rsc@golang.org>

src/strings/example_test.go

@@ -60,6 +60,28 @@ func ExampleEqualFold() {
 	// Output: true
 }
 
+func ExampleHasPrefix() {
+	fmt.Println(strings.HasPrefix("Gopher", "Go"))
+	fmt.Println(strings.HasPrefix("Gopher", "C"))
+	fmt.Println(strings.HasPrefix("Gopher", ""))
+	// Output:
+	// true
+	// false
+	// true
+}
+
+func ExampleHasSuffix() {
+	fmt.Println(strings.HasSuffix("Amigo", "go"))
+	fmt.Println(strings.HasSuffix("Amigo", "O"))
+	fmt.Println(strings.HasSuffix("Amigo", "Ami"))
+	fmt.Println(strings.HasSuffix("Amigo", ""))
+	// Output:
+	// true
+	// false
+	// false
+	// true
+}
+
 func ExampleIndex() {
 	fmt.Println(strings.Index("chicken", "ken"))
 	fmt.Println(strings.Index("chicken", "dmr"))