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.

vfs/file.go

@@ -8,6 +8,7 @@ import (
 	"time"
 
 	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/fs/log"
 	"github.com/pkg/errors"
 )
 
@@ -355,7 +356,7 @@ func (f *File) VFS() *VFS {
 //
 // We ignore O_SYNC and O_EXCL
 func (f *File) Open(flags int) (fd Handle, err error) {
-	defer fs.Trace(f, "flags=%s", decodeOpenFlags(flags))("fd=%v, err=%v", &fd, &err)
+	defer log.Trace(f, "flags=%s", decodeOpenFlags(flags))("fd=%v, err=%v", &fd, &err)
 	var (
 		write    bool // if set need write support
 		read     bool // if set need read support