This commit adds examples for Match, Find,
FindAllSubmatch, FindSubmatch and Match functions.

Change-Id: I2bdf8c3cee6e89d618109397378c1fc91aaf1dfb
GitHub-Last-Rev: 33f34b7adca2911a4fff9638c93e846fb0021465
GitHub-Pull-Request: golang/go#28837
Reviewed-on: https://go-review.googlesource.com/c/150020
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>