APR computation is not the APR defined in the market

[hyliu1989]

According to this BoA webpage, the APR is a measure to let loaner assess how expensive the up-front fee is, in the form similar to the interest rate of a loan. There is another example showing how that works which makes the concept clearer.

The APR function in the class should be updated to reflect that and the initializer to take the up-front fee into account, in my opinion.