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.

Makefile

@@ -32,8 +32,9 @@ version:
 
 # Full suite of integration tests
 test:	rclone
+	go install github.com/ncw/fstest/test_all
 	-go test $(BUILDTAGS) $(GO_FILES) 2>&1 | tee test.log
-	-cd fs && go run $(BUILDTAGS) test_all.go 2>&1 | tee test_all.log
+	-test_all github.com/ncw/rclone/fs/operations github.com/ncw/rclone/fs/sync 2>&1 | tee fs/test_all.log
 	@echo "Written logs in test.log and fs/test_all.log"
 
 # Quick test