made window mode accept shorter versions of mode name if they are unambiguous

grum/cli.py

@@ -27,9 +27,19 @@ def handle_clargs():
 
     parser.add_argument("-e", "--examples", dest="add_examples", action="store_true", help="Add example data")
 
-    parser.add_argument("-w", "--window-mode", default="multi", choices=MDIWindowMode.values(), type=str.casefold, help="Set the initial window mode")
+    parser.add_argument("-w", "--window-mode", default="multi", choices=MDIWindowMode.values(), type=unambiguous_window_mode, help="Set the initial window mode")
 
     return parser.parse_args().__dict__
 
 
 
+def unambiguous_window_mode(arg):
+    cfarg = arg.casefold()
+    values = MDIWindowMode.values()
+    matches = [i for i in values if i.casefold().startswith(cfarg)]
+    if len(matches) == 1:
+        return matches[0]
+    return arg
+
+
+