More work on nekoplunk

I've implemented the noise colour shaping as a two-pole filter (second order) rather than the simple "RC" first order filter I had before. This seems to smooth out the sound at low velocities a little better, although it could be a bit more logarithmic to stop it all being up one end.

The "Colour 2" control is used to set the resonance of the filter. It doesn't sound very good, although it's interesting. I think I'll leave it set to a low (but not zero) value to put a bit of life into the sound. I may use the same filter design in the feedback loop because it offers a bandpass as well as lowpass output. Not sure how good a bandpass filter would be here, but it's got to be worth a try.

Just as a footnote, all the development work is being done in Subversion trunk. Once I get a version that's fit to release, I'll move my development off to a branch...