Allow custom keydown handler to be attached

Fixes #118

src/xterm.js

@@ -247,6 +247,7 @@
       this.queue = '';
       this.scrollTop = 0;
       this.scrollBottom = this.rows - 1;
+      this.customKeydownHandler = null;
 
       // modes
       this.applicationKeypad = false;
@@ -2517,9 +2518,24 @@
       this.write(data + '\r\n');
     };
 
+    /**
+     * Attaches a custom keydown handler which is run before keys are processed, giving consumers of
+     * xterm.js ultimate control as to what keys should be processed by the terminal and what keys
+     * should not.
+     * @param {function} customKeydownHandler The custom KeyboardEvent handler to attach. This is a
+     *   function that takes a KeyboardEvent, allowing consumers to stop propogation and/or prevent
+     *   the default action. The function returns whether the event should be processed by xterm.js.
+     */
+    Terminal.prototype.attachCustomKeydownHandler = function(customKeydownHandler) {
+      this.customKeydownHandler = customKeydownHandler;
+    }
+
     // Key Resources:
     // https://developer.mozilla.org/en-US/docs/DOM/KeyboardEvent
     Terminal.prototype.keyDown = function(ev) {
+      if (this.customKeydownHandler && !this.customKeydownHandler(ev)) {
+        return;
+      }
       var self = this;
       var result = this.evaluateKeyEscapeSequence(ev);