MIDI.write implementation

Hi,
thank you for the library! I was wondering why there's no write implementation inside the midi class.
It's not as simple as the following, is it? 🤔
```python
def write(self, packet, num):
self.device.write(self.out_ep, packet)
```

Start in the MIDI class and inspect how input packets and endpoints are handled alongside the proposed self.device.write(self.out_ep, packet) call. Determine the required packet and num semantics, then verify that the implementation can write MIDI data through the output endpoint.

Written by the indexing model from the issue text.