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.

fs/fspath/path.go

@@ -0,0 +1,31 @@
+// Package fspath contains routines for fspath manipulation
+package fspath
+
+import (
+	"path"
+	"strings"
+)
+
+// RemoteSplit splits a remote into a parent and a leaf
+//
+// if it returns leaf as an empty string then remote is a directory
+//
+// if it returns parent as an empty string then that means the current directory
+//
+// The returned values have the property that parent + leaf == remote
+func RemoteSplit(remote string) (parent string, leaf string) {
+	// Split remote on :
+	i := strings.Index(remote, ":")
+	remoteName := ""
+	remotePath := remote
+	if i >= 0 {
+		remoteName = remote[:i+1]
+		remotePath = remote[i+1:]
+	} else if strings.HasSuffix(remotePath, "/") {
+		// if no : and ends with / must be directory
+		return remotePath, ""
+	}
+	// Construct new remote name without last segment
+	parent, leaf = path.Split(remotePath)
+	return remoteName + parent, leaf
+}