refactor how widgets are subclassed (#153)

* rework widget subclassing #121

* remove Utils.connect, add Widget.bind, Widget.connectTo

* add: types for on_event fields

* bump version to 1.5.1

* export service classes and named instance constants

* add starter config example

example/starter-config/config.js

@@ -0,0 +1,27 @@
+import { Variable } from 'resource:///com/github/Aylur/ags/variable.js';
+import { Widget } from 'resource:///com/github/Aylur/ags/widget.js';
+
+const time = new Variable('', {
+    poll: [1000, 'date'],
+});
+
+const Bar = (/** @type {number} */ monitor) => Widget.Window({
+    monitor,
+    name: `bar${monitor}`,
+    anchor: ['top', 'left', 'right'],
+    exclusive: true,
+    child: Widget.CenterBox({
+        start_widget: Widget.Label({
+            hpack: 'center',
+            label: 'Welcome to AGS!',
+        }),
+        end_widget: Widget.Label({
+            hpack: 'center',
+            binds: [['label', time]],
+        }),
+    })
+})
+
+export default {
+    windows: [Bar(0)]
+}