This program adds a PHASE list to an event dataset containing
a RAW_TIMETAG list given the ephemeris of a periodicity.
The user enters the coefficients of the ephemeris. These are:
COEFF1 - Julian date of an occurrence of phase zero (days)
COEFF2 - The periodicity at the time of COEFF1 (days)
COEFF3 - dP/dt, unitless first derivative of period wrt time