implement Y.*Binding approach

src/Binding/Binding.js

@@ -0,0 +1,15 @@
+
+import { createMutualExclude } from '../Util/mutualExclude.js'
+
+
+export default class Binding {
+  constructor (type, target) {
+    this.type = type
+    this.target = target
+    this._mutualExclude = createMutualExclude()
+  }
+  destroy () {
+    this.type = null
+    this.target = null
+  }
+}