Add general Runge-Kutta class - Add a general Runge-Kutta class which time integrates the solution based on coefficients obtained from a Butcher tableau - Add butcher tableau which returns coefficents for the specified Runge-Kutta method - Remove RungKutta4proper, since obsolete

function q = convergence(e,h)
    for i = 1:length(e)-1
        q(i) = log(e(i)/e(i+1))/log(h(i+1)/h(i));
    end
end