Add a function to set the duration that a note rings

[newlandsvalley]

Currently, notes are interpreted by players in a fairly strict legato style, A note sounds for its allotted duration and then tends to be immediately followed by the next note in the sequence. This sounds OK for some instruments but tends to sound very stilted, for example, with the grand piano. Things improved a little when I allowed notes to overlap by a tenth of the original duration. This approach should now be extended by adding a function

   setNoteRing :: forall eff. Int -> Eff (au :: AUDIO | eff) Unit

where the parameter is constrained to be a percentage of the original note duration. This allows the note to last for longer, playing alongside the next note in sequence, where 0 represents no ring at all and 100 rings for an extra whole note duration.