Implement Windows snapshotter and differ

This implements the Windows snapshotter and diff Apply function.
This allows for Windows layers to be created, and layers to be pulled
from the hub.

Signed-off-by: Darren Stahl <darst@microsoft.com>

services/diff/service_unix.go

@@ -0,0 +1,7 @@
+// +build !windows
+
+package diff
+
+var defaultDifferConfig = &config{
+	Order: []string{"walking"},
+}