change multinomial return type to be Integer[] (previously RealMatrix)



@jxwuyi 
Please review
1. added spec for int array, real array
2. fixed array sub resolution issue
3. fixed histogram for array values
4. fixed multinomial value type to be ArrayList<Integer>

@datang1992 
Please check if the getFiniteSupport is correct.

@cberzan 
FYI.
Overall good to me :+1: