In order to change the backend initialization in `global.go` to be able
to generically call cfg.ApplyEnvironment() for supported backends, the
`interface{}` returned by `ParseConfig` must contain a pointer to the
configuration.
An alternative would be to use reflection to convert the type from
`interface{}(Config)` to `interface{}(*Config)` (from value to pointer
type). However, this would just complicate the type mess further.
This change allows passing no arguments to rclone, using `-o
rclone.args=""`. It is helpful when running rclone remotely via SSH
using a key with a forced command (via `command=` in `authorized_keys`).
