Move files to src and comply with the dart package layout convention (#621)

* 👌 Use `Offset` type directly in `JoystickAction.update` calculations (#631)

* Move files to src and comply with the dart package layout convention

* Fixing widgets example

Co-authored-by: Serge Matveenko <lig@countzero.co>
Co-authored-by: Erick Zanardo <erickzanardoo@gmail.com>

lib/timer.dart

@@ -1,63 +1 @@
-import 'dart:math';
-
-/// Simple utility class that helps handling time counting and implementing
-/// interval like events.
-class Timer {
-  final double limit;
-  void Function() callback;
-  bool repeat;
-  double _current = 0;
-  bool _running = false;
-
-  Timer(this.limit, {this.callback, this.repeat = false});
-
-  /// The current amount of ms that has passed on this iteration
-  double get current => _current;
-
-  /// If the timer is finished, timers that repeat never finish
-  bool get finished => _current >= limit && !repeat;
-
-  /// Whether the timer is running or not
-  bool isRunning() => _running;
-
-  /// A value between 0.0 and 1.0 indicating the timer progress
-  double get progress => min(_current / limit, 1.0);
-
-  void update(double dt) {
-    if (_running) {
-      _current += dt;
-      if (_current >= limit) {
-        if (!repeat) {
-          _running = false;
-          callback?.call();
-          return;
-        }
-        // This is used to cover the rare case of _current being more than
-        // two times the value of limit, so that the callback is called the
-        // correct number of times
-        while (_current >= limit) {
-          _current -= limit;
-          callback?.call();
-        }
-      }
-    }
-  }
-
-  void start() {
-    _current = 0;
-    _running = true;
-  }
-
-  void stop() {
-    _current = 0;
-    _running = false;
-  }
-
-  void pause() {
-    _running = false;
-  }
-
-  void resume() {
-    _running = true;
-  }
-}
+export 'src/timer.dart';