overhaul of the chord parser

[polymorphicengine]

to make this working, i had to change TPat to a generalised ADT to add a node for TPat_Chord that essentialy has three fields, one for each component of a chord: a TPat a where a is some Num type, a TPat String for chord names and a [TPat [Modifier]] for modifiers. Due to some type trickery there is an additional field for making TPats instance of Functor (this is essentially the yoneda lemma applied, kind of like here https://stackoverflow.com/questions/17157579/functor-instance-for-a-gadt-with-type-constraint)

motivation for these changes was mainly this thread: https://club.tidalcycles.org/t/rfc-working-on-making-chord-naming-chordlist-more-consistent/2717/64

leaving the technical details behind, what these changes result in is a better seperation of syntax and semantics of chords, i.e., there is a corresponding semantic function chord :: Num a => Pattern a -> Pattern String -> [Pattern [Modifier]] -> Pattern a

further, every field in chords is patternable now and modifiers can be stacked
it should also be easy now to define new modifiers very quickly (like I did for the new drop modifier)

i also introduced two new functions collect :: Pattern a -> Pattern [a] and uncollect :: Pattern [a] -> Pattern a that collect/stack all events that have the exact same duration

[yaxu]

Looks good!

[yaxu]

Ready for merge?

[polymorphicengine]

Yes!

[yaxu]

Thanks!