* Extracting Financial Price functions for Securities - PRICE(), PRICEMAT(), PRICEDISC()
* Additional unit tests for PRICEDISC() invalid arguments
* Additional unit tests for PRICEMAT() invalid arguments
* Add docblock for PRICE()
* Clarification on validation checks for <= 0 and < 0
* Additional unit tests for previously untested financial functions, and some additions to follow untested paths
* Start splitting Financial function tests out from the large FinancialTests class into individual test classes for each function