Refactor of IRR code
New version 0.2.0
* Added Newton Method, but Bisection is still the default.
* Added new configs: precision, iteration limit.
* Raises a simple error if iteration limit is reached.
* Output is now BigDecimal.
* Fixed calculation of Bisection#npv
* Amounts in Transactions are now converted to Float
* Transactions now take Date Argument as Date instead of Time.