Add a vi keymap

This way vi users can contribute vi keybindings here and everyone
will be able to benefit.  Use "gertty -k vi" or add "keymap: vi"
to the config file.

Change-Id: Iac5db63f8f5394ab874079a6047ddc3a14ec7c22

gertty/config.py

@@ -186,7 +186,8 @@ class Config(object):
                 self.palettes[p['name']].update(p)
         self.palette = self.palettes[self.config.get('palette', palette)]
 
-        self.keymaps = {'default': gertty.keymap.KeyMap({})}
+        self.keymaps = {'default': gertty.keymap.KeyMap({}),
+                        'vi': gertty.keymap.KeyMap(gertty.keymap.VI_KEYMAP)}
         for p in self.config.get('keymaps', []):
             if p['name'] not in self.keymaps:
                 self.keymaps[p['name']] = gertty.keymap.KeyMap(p)

gertty/keymap.py

@@ -148,6 +148,13 @@ DEFAULT_KEYMAP = {
     INTERACTIVE_SEARCH: 'ctrl s',
 }
 
+# Hi vi users!  Add more things here!  This overrides the default
+# keymap, so anything not defined here will just use what's defined
+# above.
+VI_KEYMAP = {
+    QUIT: [[':', 'q']],
+}
+
 URWID_COMMANDS = frozenset((
     urwid.REDRAW_SCREEN,
     urwid.CURSOR_UP,