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 assertNumberOfArguments(fun, N)
    if nargin(fun) ~= N
        error('sbplib:assertNumberOfArguments:wrongNumberOfArguments', '"%s" must have %d, found %d', inputname(1), N, nargin(fun));
    end
end