Greatly revised/extended: greatly improved propagation for durations,
and draft versions for accessing neighbouring indices
Consecutive event indices now easily accessible with good propagation
Fixed bug in set2array (bug forced `exceeding` into `xs`)
Cleaned up (removed outdated comments etc)
Music representation constraints now organised in predicates (compared with TemporalRepresentation-singleVoice)
Added pitch representation
Added 2nd voice
Simple counterpoint example finished :)
Minor var renaming for consistency
Added variant of counterpoint example
Updated counterpoint project