A variation on the simple envelope follower

This patch is very similar to the "Simple envelope follower", with the difference that in this patch the line~ object's time of interpolation to get to a detected peak value can be different from the peakamp~ object's interval of evaluation. If, for example, the peakamp~ interval is 10 ms and the line~ ramp time is 2.5 ms, the envelope follower latency will range from only 2.5 to 12.5 ms.