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/mockobject/mockobject.go

@@ -0,0 +1,71 @@
+// Package mockobject provides a mock object which can be created from a string
+package mockobject
+
+import (
+	"errors"
+	"io"
+	"time"
+
+	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/fs/hash"
+)
+
+var errNotImpl = errors.New("not implemented")
+
+// Object is a mock fs.Object useful for testing
+type Object string
+
+// String returns a description of the Object
+func (o Object) String() string {
+	return string(o)
+}
+
+// Fs returns read only access to the Fs that this object is part of
+func (o Object) Fs() fs.Info {
+	return nil
+}
+
+// Remote returns the remote path
+func (o Object) Remote() string {
+	return string(o)
+}
+
+// Hash returns the selected checksum of the file
+// If no checksum is available it returns ""
+func (o Object) Hash(hash.Type) (string, error) {
+	return "", errNotImpl
+}
+
+// ModTime returns the modification date of the file
+// It should return a best guess if one isn't available
+func (o Object) ModTime() (t time.Time) {
+	return t
+}
+
+// Size returns the size of the file
+func (o Object) Size() int64 { return 0 }
+
+// Storable says whether this object can be stored
+func (o Object) Storable() bool {
+	return true
+}
+
+// SetModTime sets the metadata on the object to set the modification date
+func (o Object) SetModTime(time.Time) error {
+	return errNotImpl
+}
+
+// Open opens the file for read.  Call Close() on the returned io.ReadCloser
+func (o Object) Open(options ...fs.OpenOption) (io.ReadCloser, error) {
+	return nil, errNotImpl
+}
+
+// Update in to the object with the modTime given of the given size
+func (o Object) Update(in io.Reader, src fs.ObjectInfo, options ...fs.OpenOption) error {
+	return errNotImpl
+}
+
+// Remove this object
+func (o Object) Remove() error {
+	return errNotImpl
+}