Added the underscore node_module.

node_modules/underscore/cjs/mixin.js

@@ -0,0 +1,20 @@
+var underscore = require('./underscore.js');
+var each = require('./each.js');
+var functions = require('./functions.js');
+var _setup = require('./_setup.js');
+var _chainResult = require('./_chainResult.js');
+
+// Add your own custom functions to the Underscore object.
+function mixin(obj) {
+  each(functions(obj), function(name) {
+    var func = underscore[name] = obj[name];
+    underscore.prototype[name] = function() {
+      var args = [this._wrapped];
+      _setup.push.apply(args, arguments);
+      return _chainResult(this, func.apply(underscore, args));
+    };
+  });
+  return underscore;
+}
+
+module.exports = mixin;