regexp: add runnable example to regex.Split

The existing comment for regex.Split contains a plain text example,
while many of the other regex functions have runnable examples. This
change provides a runnable example for Split.

Change-Id: I5373f57f532fe843d7d0adcf4b513061ec797047
Reviewed-on: https://go-review.googlesource.com/14737Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/regexp/example_test.go

@@ -146,3 +146,25 @@ func ExampleRegexp_SubexpNames() {
 	// ${last} ${first}
 	// Turing Alan
 }
+
+func ExampleRegexp_Split() {
+	a := regexp.MustCompile("a")
+	fmt.Println(a.Split("banana", -1))
+	fmt.Println(a.Split("banana", 0))
+	fmt.Println(a.Split("banana", 1))
+	fmt.Println(a.Split("banana", 2))
+	zp := regexp.MustCompile("z+")
+	fmt.Println(zp.Split("pizza", -1))
+	fmt.Println(zp.Split("pizza", 0))
+	fmt.Println(zp.Split("pizza", 1))
+	fmt.Println(zp.Split("pizza", 2))
+	// Output:
+	// [b n n ]
+	// []
+	// [banana]
+	// [b nana]
+	// [pi a]
+	// []
+	// [pizza]
+	// [pi a]
+}