Make distinction between root finding algorithm and function clearer

[sverhoeven]

At the moment the x^3 - x^2 + 2 function and its derivative are hard to distinguish from the root finding algorithm. It would be nice if the function + derivative could be moved to their own code block
So it is clearer we are trying to find the root of the x^3 - x^2 + 2 function with the Newton-Raphson algorithm.

[sverhoeven]

And rename func to equation and derivFunc to derivative.

[fdiblen]

also rename find to solve.