Real time tunable filters

A library of first and second order filters whose parameters can be tuned in real-time.

The transfer function of different filters has been drawn as a signal flow diagram, thereby exposing the center frequency and Q of the filter coefficients. These parameters can now be easily tuned on a real-time system, e.g. on a dSPACE platform, without having to recompile the model in order to change the filter parameters. Advantages of this filter are:
- it can handle a vectorized input, i.e. muxed signals;
- A reset signal can easily be added to the integrators.