freddyH / Finance_NumberOfPeriods / 0.1.0
NPER(rate, PMT, PV, FV, type). Returns the number of periods for an investment based on periodic,constant payments and a constant interest rate. 
 * Rate is the periodic interest rate. 
 * PMT is the constant annuity paid in each period. 
 * PV is the present value (cash value) in a sequence of payments. 
 * FV (optional) is the future value, which is reached at the end of the last period. 
 * Type (optional) defines whether the payment is due at the beginning (1) or the end (0) of a period.