Added polynomial multiplication and inverse operator routines.

operator: added compute_omegap and compute_operator_inverse

utility: added mpoly and mpolyr to multiply polynomials (and restrict to
below some degree threshold in case of mpolyr). Also added MIN macro.

main: added items to menu and calls to test drivers.
Added code to compute A^2B^2 during omega' routine

Operator: updated compute_omegap to multiply B^2 and A^2
Utility: changed loop initializing C to use <= instead of <