rework events

• ManualTrigger/TimeTrigger should be reworked as EventLoop. Every EventLoop is coupled with a ResourceOwner.
• An EventLoop can have multiple FileDescriptors associated, but only one timer.
• By default the EventLoop will continue working until explicitly stopped (this is different from previous EventPool events, which had to be re-enabled).

The interface:

class Something : public ResourceOwner {
  EventLoop loop;

  void setup() {
    loop.setup(Ref(this), {fileDescriptor, anotherFileDescriptor}); // using a Deque list of pointers
  }

  void event(EventLoop::Control& ev) {
    if (fileDescriptor(ev).read().triggered()) {
    }
    control.timeOutIn(500_ms) or control.timeOutAt(absoluteTime);
    control.stop();
  }

  void someOtherFuncRunningOnResourceOwner() {
    control.ensure(this); // starts if stop() is called before on control
  }
};

Additional interfaces:

• FileDescriptor::reset(int fd)
• EventLoop::add(FileDescriptor&) (and remove)