Converts this date-time to the number of seconds from the epoch
of 1970-01-01T00:00:00Z.
!(p)
This uses the {@linkplain #toLocalDateTime() local date-time} and
{@linkplain #getOffset() offset} to calculate the epoch-second value,
which is the number of elapsed seconds from 1970-01-01T00:00:00Z.
Instants on the time-line after the epoch are positive, earlier are negative.
@return the number of seconds from the epoch of 1970-01-01T00:00:00Z
Converts this date-time to the number of seconds from the epoch of 1970-01-01T00:00:00Z. !(p) This uses the {@linkplain #toLocalDateTime() local date-time} and {@linkplain #getOffset() offset} to calculate the epoch-second value, which is the number of elapsed seconds from 1970-01-01T00:00:00Z. Instants on the time-line after the epoch are positive, earlier are negative.
@return the number of seconds from the epoch of 1970-01-01T00:00:00Z