Created TaxRate value object class to use in StockMarketYear

Code as end of session 14
Integrated TaxRate and InterestRate (newly created) into StockMarketYear
Created a value object class Dollars and started integrating into StockYearMarket

Code as end of session 17
TaxRate and InterestRate are now working in Dollars

Dollars has been fully integrated into StockMarketYear

Fully de-Primitive obsession code as end of session 18