Add open, inv and drop function

[thgrund]

I would like to discuss these three new functions. I wanted to use inversions and drop chords independently from the chord notation in the mini notation and came up with this solution.

My motivation comes from my system where I create harmonies and melodies in a totally different approach then we usually do in TidalCycles: https://github.com/thgrund/mrreason-setup/blob/main/README.md

But I think these functions (open, drop and inv) could be useful in general.

[thgrund]

And I realize that I need to change the name of the functions because of ambiguity