Add module for Scheduler.

Also reorganizes some code to make it easier to add more modules.

src/module/scheduler.wren.inc

@@ -0,0 +1,28 @@
+// Generated automatically from src/module/scheduler.wren. Do not edit.
+static const char* schedulerModuleSource =
+"class Scheduler {\n"
+"  static add(callable) {\n"
+"    if (__scheduled == null) __scheduled = []\n"
+"\n"
+"    __scheduled.add(Fiber.new {\n"
+"      callable.call()\n"
+"      runNextScheduled_()\n"
+"    })\n"
+"  }\n"
+"\n"
+"  // Called by native code.\n"
+"  static resume_(fiber) { fiber.transfer() }\n"
+"  static resume_(fiber, arg) { fiber.transfer(arg) }\n"
+"\n"
+"  static runNextScheduled_() {\n"
+"    if (__scheduled == null || __scheduled.isEmpty) {\n"
+"      return Fiber.suspend()\n"
+"    } else {\n"
+"      return __scheduled.removeAt(0).transfer()\n"
+"    }\n"
+"  }\n"
+"\n"
+"  foreign static captureMethods_()\n"
+"}\n"
+"\n"
+"Scheduler.captureMethods_()\n";