Intermediate; signatures and rough functions for conversion of
polynomials between semirings prepared.
Tried to build converter methods for polynomials over one semiring to
such over another. Failed because of access modifiers in the
poly-/monomials and because there's no way to build an element of one
semiring from an element of another semiring without major changes.
Simple way for dealing with new semirings seems to be writing a new
parser.