wrong values in metrical strength features

[sildater]

the metrical strength features in note_features.py return four attributes:

"beat_phase",
"metrical_strength_downbeat",
"metrical_strength_secondary",
"metrical_strength_weak"

metrical_strength_downbeat and metrical_strength_weak return 1.0 in the presence of a downbeat which seems wrong for the latter, line 1066 is probably the problem. A bit of documentation on each feature is also missing (what is secondary, what is weak, does it work for triple meters?).

[manoskary]

Hello, thanks for the issue. These features are taken from the basis functions of the basis mixer. Some documentation that could always be useful, I can look into it. But maybe @neosatrapahereje would be the best person to write the documentation for that or review the resulting PR.

[sildater]

I could also fix, I already know where it is.