No compression support in MusicDataset

[cifkao]

MusicDataset doesn't seem to support loading compressed files (#39). Neither kind="json" nor kind="json.gz" works.

[cifkao]

Here is a workaround:

class MusicDataset(muspy.datasets.MusicDataset):

    def __init__(self, root: Union[str, Path], kind: str = "json", suffix: str = "json"):
        super().__init__(root=root, kind=kind)
        self.filenames = sorted(self.root.rglob("*." + suffix))

dataset = MusicDataset('data/', kind='json', suffix='json.gz')