Break the fs package up into smaller parts.

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.

fs/config/config_other.go

@@ -0,0 +1,10 @@
+// Read, write and edit the config file
+// Non-unix specific functions.
+
+// +build !darwin,!dragonfly,!freebsd,!linux,!netbsd,!openbsd,!solaris
+
+package config
+
+// attemptCopyGroups tries to keep the group the same, which only makes sense
+// for system with user-group-world permission model.
+func attemptCopyGroup(fromPath, toPath string) {}