fix some tests, implement event classes for types, and re-implement logging

src/Transaction.js

@@ -0,0 +1,24 @@
+
+export default class Transaction {
+  constructor (y) {
+    this.y = y
+    // types added during transaction
+    this.newTypes = new Set()
+    // changed types (does not include new types)
+    // maps from type to parentSubs (item.parentSub = null for array elements)
+    this.changedTypes = new Map()
+  }
+}
+
+export function transactionTypeChanged (y, type, sub) {
+  if (type !== y && !type._deleted) {
+    const changedTypes = y._transaction.changedTypes
+    let subs = changedTypes.get(type)
+    if (subs === undefined) {
+      // create if it doesn't exist yet
+      subs = new Set()
+      changedTypes.set(type, subs)
+    }
+    subs.add(sub)
+  }
+}