- Added salaryYTD, taxWithheldYTD, and deductionsYTD to PayStub table &
class
- Added $afterDate and $beforeDate optional filter parameters to
DBInterface::readPayStubs() for restricting the returned set to be
within a date range.  Used for retrieving the previous pay stub for an
employee in the current year.
- When generating paystubs, retrieve the previous YTD amounts.