Business and Financial Day Calculators.

The DateCalculator implementation is useful to any business; the other two
interfaces are more specific to the financial industry.

The most common function of a lot of banking or business applications is the
handling of holidays and weekends, a set of standard rules are implemented to deal with days falling on a holiday. The library does not attempt to guess the 'holidays', most business will have an official list anyway, but concentrate on the date manipulation and calculations.

What does it provide? Implementation of 3 interfaces
- DateCalculator for all date calculation and handling of weekends or holidays.
The supported algorithms are: Do Nothing, Move Forward, Move Backward,
Modified Following and Modified Preceeding.