Add an option to control the accuracy of FindRoot function.

[tranleduy2000]

Dear @axkr The current implementation of the FindRoot uses default constructor of numeric solver classes, which has default accuracy = 1e-6

public class NewtonRaphsonSolver extends AbstractUnivariateDifferentiableSolver {
    /** Default absolute accuracy. */
    private static final double DEFAULT_ABSOLUTE_ACCURACY = 1e-6;

    /**
     * Construct a solver.
     */
    public NewtonRaphsonSolver() {
        this(DEFAULT_ABSOLUTE_ACCURACY);
    }

Could you please add an option to allow us control the accuracy of FindRoot function?