Allow more extreme exponential curves in advanced mode

[w-winter]

This proposal affects only non-looping ramp segments.

In the standard segment generator mode, we get the same (as stock firmware) accelerating => linear => decelerating range of curves across the upper pot's travel.

In the advanced segment generator mode, this pot exhibits the same behavior for the first 50% of its turn but reaches the default exponential curve at around 2:30 o'clock and after that point bends into increasingly hyperexponential curves. I find that this facilitates dialing in envelopes with decay tails that sound more "natural" in how they ring out, much like the response of a nice vactrol. It should be particularly useful to people who only use linear VCAs and so need more control over their envelope's shape at its source.