A solver for every quadratic

Write a quadratic solver that never gives up, and a function for square roots of complex numbers. Use math.sqrt only, so you see where the $i$ comes from.

The idea. When $D < 0$, the roots are $\dfrac{-b \pm i\sqrt{-D}}{2a}$. In Python, complex(p, q) is the number $p + qi$.

Your tasks.

1. In discriminant, return $b^2 - 4ac$.
2. In roots, return both roots: real numbers when $D$ is not negative, and complex numbers when it is. Put the root with the plus sign first.
3. In square_root, return the square root $x + iy$ of $p + iq$ whose real part $x$ is not negative.