--one-way argument will check that all files on source matches the files on detination,
but not the other way. For example files present on destination but not on source will not
trigger an error.
Fixes: #1526
The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.
The new code layout is documented in CONTRIBUTING.
