Date at each projection step.

Returns a date representing each projection step as pandas Timestamp. date_(0) is read from date_init. For i > 0, date_(i) is defined recursively as:

date_(i-1) + offset(i-1)

date_(i) must always return an end-of-month date. The length of each projection step is specified by offset(). Items indexed with i and representing the change of a quantity in a projection period such as cashflows, represents the change during the projection period starting from one day after date_(i) and ending on date_(i+1)