Otherwise you can create multiple drivers on the same singleton like this:

```rust
let mut input = Input::new(&pin, Pull::None);
let mut output = Output::new(&pin, Level::Low, Speed::Low);
input.is_high();
output.set_high();
input.is_high();
output.set_high();
```

Thanks @pennae for reporting.

fixes #1316.

This allows a writer to access all of the free space in the buffer, even
when it's wrapping around.

This allows the ringbuf to be filled up to `N` instead of just `N-1`, using some fun tricks on the indices.

The advantage is better performance: Before, the first write would fill N-1 bytes, The second would write just the 1 byte left before wrapping, then N-2. Then 2, then N-3, and so on. This would result in more smaller chunks, so worse perf. This problem is gone now.