…py.ndarray.__format__`

This fixes `AttributeError: module 'scipy.signal' has no attribute 'hann'` that occurs when trying to augment data using `automix.py`.

In librosa version 0.10.2.dev0, the `__trim_beats` in beat.py no longer uses scipy for hanning computation & now uses `np.hanning` instead.

Fix README.md instructions for machine learning scientists, so that the training requirements/dependencies actually get installed.

`-12` should have been `-0.12` but the comment was redundant, so I removed it.