strconv: reformat and tidy comments in example

Apply the suggestions made in the too-late review of
	golang.org/cl/137215
to move the comments to a separate line and use proper
punctuation.

Change-Id: If2b4e5ce8af8c78fa51280d5c87c852a76dae459
Reviewed-on: https://go-review.googlesource.com/c/go/+/206125Reviewed-by: Robert Griesemer <gri@golang.org>

src/strconv/example_test.go

@@ -294,7 +294,8 @@ func ExampleParseUint() {
 }
 
 func ExampleQuote() {
-	s := strconv.Quote(`"Fran & Freddie's Diner	☺"`) // there is a tab character inside the string literal
+	// This string literal contains a tab character.
+	s := strconv.Quote(`"Fran & Freddie's Diner	☺"`)
 	fmt.Println(s)
 
 	// Output:
@@ -338,7 +339,8 @@ func ExampleQuoteRuneToGraphic() {
 }
 
 func ExampleQuoteToASCII() {
-	s := strconv.QuoteToASCII(`"Fran & Freddie's Diner	☺"`) // there is a tab character inside the string literal
+	// This string literal contains a tab character.
+	s := strconv.QuoteToASCII(`"Fran & Freddie's Diner	☺"`)
 	fmt.Println(s)
 
 	// Output:
@@ -349,7 +351,8 @@ func ExampleQuoteToGraphic() {
 	s := strconv.QuoteToGraphic("☺")
 	fmt.Println(s)
 
-	s = strconv.QuoteToGraphic("This is a \u263a	\u000a") // there is a tab character inside the string literal
+	// This string literal contains a tab character.
+	s = strconv.QuoteToGraphic("This is a \u263a	\u000a")
 	fmt.Println(s)
 
 	s = strconv.QuoteToGraphic(`" This is a ☺ \n "`)