Added support for Poly(f, x, y).coeff(x*y)
update coeff-related docstrings; special case Poly in coeff
change Poly.coeff to Poly.monomial_coeff
change monomial_coeff to coeff_monomial
edit docstrings
Poly.coeff is NotImplemented
Try to fix Sphinx error
Merge pull request #1812 from smichr/poly-coeffs

Poly coeffs