Added geturl() method (#289)

Author: zmej-serow

fs/ftpfs.py

@@ -453,6 +453,13 @@ def ftp(self):
         """~ftplib.FTP: the underlying FTP client.
         """
         return self._get_ftp()
+    
+    def geturl(self, path, purpose="download"):
+        # type: (str, str) -> Text
+        """Get FTP url for resource."""
+        if purpose != "download":
+            raise errors.NoURL(path, purpose, "No such purpose")
+        return "{}/{}".format(self.ftp_url, path)
 
     def _get_ftp(self):
         # type: () -> FTP