scripts: Tweaked -./-p/-P flags in ascii scripts

- -*/--add-char/--chars -> -./--add-char/--chars
- -./--points -> -p/--points
- -!/--points-and-lines -> -P/--points-and-lines

Also fixed an issue in plot.py/Attr where non-list default were failing
to concatenate.

scripts/plotmpl.py

@@ -305,7 +305,7 @@ class Attr:
                     not isinstance(attr, tuple)
                         or attr[0] in {None, (), ('*',)}
                     for attr in (attrs or []))):
-            attrs = defaults + (attrs or [])
+            attrs = list(defaults) + (attrs or [])
 
         # normalize
         self.attrs = []
@@ -1341,11 +1341,11 @@ if __name__ == "__main__":
                 "specific group where a group is the comma-separated 'by' "
                 "fields. Accepts %% modifiers.")
     parser.add_argument(
-            '-.', '--points',
+            '-p', '--points',
             action='store_true',
             help="Only draw data points.")
     parser.add_argument(
-            '-!', '--points-and-lines',
+            '-P', '--points-and-lines',
             action='store_true',
             help="Draw data points and lines.")
     parser.add_argument(