Migrating from version 3

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Version 4 makes transactions safe by default, reports availability the way a user interface needs it, and checks the state of actions. Update your code as follows:

Version 3	Version 4
`CreateTransaction(bool isDelayed = true)`	`CreateTransaction(TransactionExecutionMode mode = TransactionExecutionMode.Deferred)`. `isDelayed: true` is Deferred, `isDelayed: false` is Immediate.
Disposing a transaction committed it	Disposing rolls it back unless CommitAsync was called. Call `await transaction.CommitAsync()` before leaving the scope.
Nesting transactions with different `isDelayed` values	Throws an `InvalidOperationException`: a nested transaction uses the mode of the enclosing one.
`UndoRedoManager.CommitTransactionAsync()` and `RollbackTransactionAsync()`	Removed: they completed the innermost transaction, whichever handle the caller held. Call `transaction.CommitAsync()` or `transaction.RollbackAsync()`.
`CollectionChanged`	HistoryChanged. UndoRedoManager also implements `INotifyPropertyChanged`.
CanUndo and CanRedo reported the content of the histories	They report whether the operation would succeed, so they are `false` while a transaction is open or an action runs.
`UndoRedoActionBase.ExecuteCount`	IsApplied. Executing an applied action, or reverting an action that is not applied, throws instead of doing nothing.
A canceled `CancellationToken` was only passed to the action	Every operation throws an `OperationCanceledException` before running anything.
A `CollectionChanged` handler that threw looked like a failure of the operation	The exception is wrapped in an UndoRedoNotificationException, thrown after the operation completed.
Unbounded history	Still the default. Pass `maxHistoryDepth` to the constructor to bound it.

See Transactions and Undo history in the UI for the details.