x/tools/cmd/godoc: Examples should be followed by blank a newline

before the beginning of another function.

For example, a snippet in `godoc -ex strings` would change from

<
func Contains(s, substr string) bool
    Contains reports whether substr is within s.

    Example:
        fmt.Println(strings.Contains("seafood", "foo"))
        fmt.Println(strings.Contains("seafood", "bar"))
        fmt.Println(strings.Contains("seafood", ""))
        fmt.Println(strings.Contains("", ""))
        // Output:
        // true
        // false
        // true
        // true
func ContainsAny(s, chars string) bool
    ContainsAny reports whether any Unicode code points in chars are within
    s.

    Example:
        fmt.Println(strings.ContainsAny("team", "i"))
        fmt.Println(strings.ContainsAny("failure", "u & i"))
        fmt.Println(strings.ContainsAny("foo", ""))
        fmt.Println(strings.ContainsAny("", ""))
        // Output:
        // false
        // true
        // false
        // false
func ContainsRune(s string, r rune) bool
>

to

<
func Contains(s, substr string) bool
    Contains reports whether substr is within s.

    Example:
        fmt.Println(strings.Contains("seafood", "foo"))
        fmt.Println(strings.Contains("seafood", "bar"))
        fmt.Println(strings.Contains("seafood", ""))
        fmt.Println(strings.Contains("", ""))
        // Output:
        // true
        // false
        // true
        // true

func ContainsAny(s, chars string) bool
    ContainsAny reports whether any Unicode code points in chars are within
    s.

    Example:
        fmt.Println(strings.ContainsAny("team", "i"))
        fmt.Println(strings.ContainsAny("failure", "u & i"))
        fmt.Println(strings.ContainsAny("foo", ""))
        fmt.Println(strings.ContainsAny("", ""))
        // Output:
        // false
        // true
        // false
        // false

func ContainsRune(s string, r rune) bool
>

Fixes: golang/go#13053

Change-Id: I355870b1e90b2b6ca0104d67e85869593f294252
Reviewed-on: https://go-review.googlesource.com/16329
Reviewed-by: Andrew Gerrand <adg@golang.org>

godoc/godoc.go

@@ -434,7 +434,7 @@ func (p *Presentation) example_textFunc(info *PageInfo, funcName, indent string)
 		buf.WriteString(indent)
 		buf.WriteString("Example:\n\t")
 		buf.WriteString(code)
-		buf.WriteString("\n")
+		buf.WriteString("\n\n")
 	}
 	return buf.String()
 }