Function calculate_amortization_loan

calculate_amortization_loan(
    principal: number,
    apr: number,
    months: number,
    extra_monthly_payments?: ExtraPaymentInformation[],
    fixed_payment?: boolean,
    digits?: number,
): Readonly<AmortizationLoan>
Calculates loan information using the amortization formula

Note: This is akin to a mortgage calculator
Parameters
- principal: number
  the starting principal of the loan
- apr: number
  the interest rate of the loan
- months: number
  the number of months for the loan
- extra_monthly_payments: ExtraPaymentInformation[] = []
  an array of extra payments made towards the loan
- fixed_payment: boolean = true
  if set to false, will allow the monthly payment to reduce over time, otherwise it remains fixed like a mortgage-style loan
- digits: number = 2
  the number of digits to round the result to
Returns Readonly<AmortizationLoan>