runes: added spanner implemenation

Change-Id: Ifa7d61c682b2347ea6111910c0955ec2a2501930
Reviewed-on: https://go-review.googlesource.com/29185
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>
4 files changed