Add special cases of double quotes: eg {{url}}

This allows a second level of indirection quite cheaply, but is a
band-aid fix.

This commit should be taken as temporary until command arguments are
reworked.

qutebrowser/commands/runners.py

@@ -65,10 +65,10 @@ def replace_variables(win_id, arglist):
             QUrl.DecodeReserved | QUrl.RemovePassword),
         'clipboard': utils.get_clipboard,
         'primary': lambda: utils.get_clipboard(selection=True),
-        'suburl': lambda: '{url}',
+        '{url}': lambda: '{url}',
-        'suburl:pretty': lambda: '{url:pretty}',
+        '{url:pretty}': lambda: '{url:pretty}',
-        'subclipboard': lambda: '{clipboard}',
+        '{clipboard}': lambda: '{clipboard}',
-        'subprimary': lambda: '{primary}',
+        '{primary}': lambda: '{primary}',
     }
     values = {}
     args = []