To find the residues, poles, and direct term of a Partial Fraction Expansion
of the ratio of two polynomials, where the expansion is of the form
\frac{b_2s^2+b_1s+b_0}{a_2s^2+a_1s+a_0}
[r,p,k] = residue(b,a)

To convert the partial fraction expansion back to the ratio of two polynomials
and return the coefficients in b and a.
[b,a] = residue(r,p,k)

Example:
b = [-4 8];
a = [1 6 8];
[r,p,k] = residue(b,a)