Allow disable default key bindings

Default (OSX).sublime-keymap

@@ -1 +1,15 @@
-[{ "keys": ["ctrl+u"], "command": "open_url" }]
+[
+  {
+    "keys": [
+      "ctrl+u"
+    ],
+    "command": "open_url",
+    "context": [
+      {
+        "key": "setting.open_url.disable_default_key_bindings",
+        "operator": "not_equal",
+        "operand": true
+      }
+    ]
+  }
+]

Default.sublime-keymap

@@ -1,2 +1,16 @@
 // Linux and Windows
-[{ "keys": ["ctrl+alt+u"], "command": "open_url" }]
+[
+  {
+    "keys": [
+      "ctrl+alt+u"
+    ],
+    "command": "open_url",
+    "context": [
+      {
+        "key": "setting.open_url.disable_default_key_bindings",
+        "operator": "not_equal",
+        "operand": true
+      }
+    ]
+  }
+]

README.md

@@ -191,6 +191,10 @@ Some settings, especially the URL / path transforms like `aliases`, will probabl
 
 Project-specific settings override default and user settings.
 
+### Disable default key bindings
+
+To do this, add `"open_url.disable_default_key_bindings": true` to `Preferences.sublime-settings`.
+
 ## Release Notes
 
 [See Open URL's version history here](https://github.com/noahcoad/open-url/tree/master/messages).