timer.Seq() specifies a sequence that is an arbitrary sequence
of beats. timer.Seq() also takes a ghost beat (5) that does not form
part of the sequence. We will see why a ghost beat is useful later.
$ go run sequence-seq.go
[
{"_time":0,"_type":12,"_value":1},
{"_time":1.5,"_type":12,"_value":1},
{"_time":2,"_type":12,"_value":1},
{"_time":4,"_type":12,"_value":1}
]