fmt: unify the printing examples
fmt: unify the printing examples

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/136615
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

golang/go,akutz/go,CAFxX/go,nawawi/go,cloudflare/go,nawawi/go,josharian/go,golang/go,josharian/go,golang/go,CAFxX/go,josharian/go,nawawi/go,CAFxX/go,akutz/go,golang/go,nawawi/go,golang/go,josharian/go,CAFxX/go,cloudflare/go,akutz/go,akutz/go,cloudflare/go,nawawi/go,cloudflare/go,akutz/go,josharian/go,josharian/go,cloudflare/go,cloudflare/go,akutz/go,CAFxX/go,CAFxX/go,nawawi/go,josharian/go,nawawi/go,akutz/go,josharian/go,CAFxX/go,akutz/go,golang/go,nawawi/go,cloudflare/go,golang/go,golang/go,cloudflare/go,CAFxX/go