I wish that `BeEmpty()` would list the items when not empty

```
// "Expected collection to be empty, but found 3."
new[] {1, 2, 3}.Should().BeEmpty();
```

I wish the message included the list of items. Instead, I use:

```
// "Expected collection {1, 2, 3} to be equivalent to {empty}, but it contains too many items."
new[] {1, 2, 3}.Should().BeEquivalentTo(Enumerable.Empty<int>());
```
