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 A = kr(varargin)
    n = nargin;

    A = 1;

    for i = 1:n
        A = kron(A,varargin{i});
    end
end