Precision of square eq solver can be improved for a->0

[stiv-yakovenko]

HI! Instead of using (-b+-sqrt(d))/2/a you can use this formulae to get rid of 0/0 division in case a->0:

    sqD = sqrt(d);
    x1 = b > 0 ? (2 * c / (-b - sqD)) : (2 * c / (-b + sqD));
    x2 = -b / a - x1;

Thanx.

[vorot]

A good point indeed, thank you. There are even more things to take into account as described in https://people.csail.mit.edu/bkph/articles/Quadratics.pdf

I am not sure when I have time time for this change but I shall accept a pull request if you dare to change the code yourself (tests are welcome too).

[vorot]

Fixed in v0.0.4