Classified new version

let cmin = Scale.minor(key: .c)

updated with

let min = ScaleType.min // enum
let cmin = Scale(type: min, key: .c) // struct

style for all Note, Scale and Chord types.
We have NoteType, ScaleType and ChordType enums, key and octave agnostic.
We have Note, Scale and Chord structs with keys and octaves as well as some handy operation functions.