Add support for artificial viscosity to the 1d burgers scheme. - Add support for artificial viscosity by parametrizing the discretization operator and boundary closure on the viscosity. - Add a time stepper which evaluates and updates the residual viscosity of the solution.

function assertType(obj, type)
    if ~isa(obj, type)
        error('sbplib:assertType:wrongType', '"%s" must have type "%s", found "%s"', inputname(1), type, class(obj));
    end
end