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

% Assert that array A has the size s.
function assert_size(A,s)
    warning('Use assertSize() instead!')
    assertSize(A,s);
end