Move things around for gb

This moves all restic source files to src/, and all vendored
dependencies to vendor/src.

doc.go

@@ -1,6 +0,0 @@
-// Package restic is the top level package for the restic backup program,
-// please see https://github.com/restic/restic for more information.
-//
-// This package exposes the main components needed to create and restore a
-// backup as well as handling things like a local cache of objects.
-package restic