Objects to manipulate sequential and seasonal time series. Sequential time
series based on time instants and time durations are handled. Both can be
regularly or unevenly spaced (overlapping durations are allowed).
Only POSIX* format are used for dates and times.
The following classes are provided : POSIXcti, POSIXctp,
TimeIntervalDataFrame, TimeInstantDataFrame, SubtimeDataFrame ;
methods to switch from a class to another and to modify the time support
of series (hourly time series...