Viewcpd

Added a method that creates and populates a Pandas dataframe with the all the assignments to all the random variables involved in the CPD, along with the conditional probabilities for each assignments.

The CPD for "Grade" in the default example gets printed this way:

	    Grade	Letter	probability
        0	 A	 weak	 0.10
        1	 A	 strong	 0.90
        2	 B	 weak	 0.40
        3	 B	 strong	 0.60
        4	 C	 weak	 0.99
        5	 C	 strong	 0.01