DiceChecker done.

Finished DicChecker interface.
RollManager interface

Added RollManager interface with methods, but not documentation.
RollManager documentation.

Added documentation to the RollManager interface.
RollSession interface

Added RollSession interface with methods and documentation.
JUnit + D6

Added JUnit to build path.
Added D6 test cases and implementation.
D6 documentation

Added documentation to the D6 class.