Provide an example for each of the printing functions (Print,
Sprintf, Fprintln etc.), and make them all produce the same output
so their usage can be compared.

Also add a package-level example explaining the difference between
how Printf, Println, and Print behave.

There are more examples to come.

Update #27554.

Change-Id: Ide03e5233f3762a9ee2ac0269f534ab927562ce2
Reviewed-on: https://go-review.googlesource.com/136615Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>