Package app contains some logic that we want to share with gobind-based libraries. So move it to a new internal package that both can import. Long term the log changes should be in the standard library, but the Go tree is currently frozen. Fixes golang/go#11630. Change-Id: I9ff622fc499bf255bce18df23cb68b03f667947f Reviewed-on: https://go-review.googlesource.com/11981 Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>