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

# SBPLIB
sbplib is a library of primitives and help functions for working with summation-by-parts finite differences in Matlab. To use sbplib download the code and add the sbplib folder to the matlab path.