MoveDirectory and CopyDirectory with overwrite

Please support overwriting with `MoveDirectory` and `CopyDirectory`.

A bool parameter in the third position would make sense, wouldn't it? This seems common enough and similar enough to other APIs:

```c#
MoveDirectory(fromPath, toPath, true);
CopyDirectory(fromPath, toPath, false);
```

Or should an entire options class be created in order to specify `Overwrite`?