Publishing MUSCIMA++ measure annotation dataset
In this release, we added a derived datasest from the MUSCIMA++ dataset, that contains annotations for staves, system measures and stave measures.
Further changes:
- Improved the documentation, so readthedocs actually renders the content properly.
- Significantly improved the download-progress reporting by resorting to TQDM instead of simply printing lines.
- Dropping Python 3.5 support, because we're using string-interpolation