Returns a ti for the current date.
today(tif = "daily")a ti Frequency, given as either a numerical code or a string.
tif() with no arguments returns a list of the allowable
numerical codes and names. The default "daily" returns a ti
object for the current day.
A ti object of the specified ti frequency that contains the
current date in the time interval it represents. For example, if
tif is "monthly", the returned ti object will
be for the current month.