add mo_polynomial with tests

This new module provides routines to deal with polynomials like evaluation, root finding or derivation.

Polynomials of order (n-1) are represented by an array of n coefficients p = (p_1, p_2, ..., p_n) starting with the coefficient for the biggest exponent:

P(x) = p_1 * x^(n-1) + p_2 * x^(n-2) ... + p_n

The following routines are implemented:

• poly_eval: evaluate a polynomial at a point
• poly_deriv: derive a polynomial
• poly_order: determine the order of the polynomial
• poly_root: find root of a polynomial with different methods (0 - Auto, 1 - Newton, 2 - Halley (default for order > 1), 3 - cubic Householder)