New symbolic parameter creation function for Stone-Holmes distribution with assumptions

Generates symbolic parameters, Delta, Epsilon, Lambda_U, and Lambda_S for use with solving symbolic equations. Assumptions are generated as well.

A copy of validateindex() is now in the stonesholmes private directory.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>
Removed symbolic assumption for approximation

An assumption corresponding to the Stone-Holmes approximation was removed.

Signed-off-by: Andrew D. Horchler <adh9@case.edu>