example: add windows batch files

Add windows batch files to build and run examples

Change-Id: I9102ceb5c47f692730a8b024648b1d10ff49b624
Reviewed-on: https://go-review.googlesource.com/1622
Reviewed-by: David Crawshaw <crawshaw@golang.org>
example/sprite: make example lives

Add necessary files to build and run example/sprite.
Change main.go to get image from assets.

Change-Id: Ic3065aab97f59c34f2c0446ab4b46840305b5864
Reviewed-on: https://go-review.googlesource.com/1882
Reviewed-by: David Crawshaw <crawshaw@golang.org>