Add vim 'dd' binding.

lib/ace/keyboard/keybinding/vim.js

@@ -46,6 +46,10 @@ var vimStates = {
             key:    "i",
             then:   "insertMode"
         },
+        {
+            key:    "d",
+            then:   "deleteMode"
+        },
         {
             key:    "a",
             exec:   "gotoright",
@@ -160,6 +164,13 @@ var vimStates = {
             exec:     "overwrite",
             then:     "start"
         }
+    ],
+    deleteMode: [
+        {
+            key:      "d",
+            exec:     "removeline",
+            then:     "start"
+        }
     ]
 };