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.

fstest/mockdir/dir.go

@@ -0,0 +1,13 @@
+// Package mockdir makes a mock fs.Directory object
+package mockdir
+
+import (
+	"time"
+
+	"github.com/ncw/rclone/fs"
+)
+
+// New makes a mock directory object with the name given
+func New(name string) fs.Directory {
+	return fs.NewDir(name, time.Time{})
+}