Improve Performance and Improve generalization

[ausaf007]

Performance Enhancement:

• Replace mod().pow() to modPow() in Peggy class

Generalization

• Abstract out the code from Peggy class, and create a Prover class. Make Peggy an instance of this Prover class.
• Abstract out the code from Victor class, and create a Verifier class. Make Victor an instance of this Verifier class.
• Change random4() to random(int digits), to generate any arbitrary digit random number.