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/write.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/ncw/rclone/fs"
+	"github.com/ncw/rclone/fs/operations"
 )
 
 // WriteFileHandle is an open for write handle on a File
@@ -64,7 +65,7 @@ func (fh *WriteFileHandle) openPending() (err error) {
 	pipeReader, fh.pipeWriter = io.Pipe()
 	go func() {
 		// NB Rcat deals with Stats.Transferring etc
-		o, err := fs.Rcat(fh.file.d.f, fh.remote, pipeReader, time.Now())
+		o, err := operations.Rcat(fh.file.d.f, fh.remote, pipeReader, time.Now())
 		if err != nil {
 			fs.Errorf(fh.remote, "WriteFileHandle.New Rcat failed: %v", err)
 		}