Added Contour.count_distinct_roots
Added Contour.count_distinct_roots

Computes the number of distinct roots within a contour as the rank of
the NxN Hankel matrix defined in section 1.2 of "Computing the zeros of
analytic functions" by Peter Kravanja, Marc Van Barel, Springer 2000

rparini/cxroots,rparini/cxroots