It was a little tricky to figure out how to go from the documentation
to figuring out the best way to implement a Pool, so I thought I'd
try to provide a simple example. The implementation is mostly taken
from the fmt package.

I'm not happy with the verbosity of the calls to WriteString() etc,
but I wanted to provide a non-trivial example.

Change-Id: Id33a8b6cbf8eb278f71e1f78e20205b436578606
Reviewed-on: https://go-review.googlesource.com/24371Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>