This function returns the h-vector of M, i.e., the
coefficients of the numerator of the simplified Poincare series for M.
M can be a module or a quotient.
The weights of the indeterminates of the polynomial ring of M must all be 1,
and the coefficient ring must be a field.
If the input is not homogeneous, the Hilbert function of the
corresponding leading term (initial) ideal or module is calculated.