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.
Fixesgolang/go#11630.
Change-Id: I9ff622fc499bf255bce18df23cb68b03f667947f
Reviewed-on: https://go-review.googlesource.com/11981
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>