envy24control: enhanced mapping of midi controller

envy24control: enhanced mapping of midi controller
From: Dirk Jagdmann <doj@cubic.org>

Hello,

this patch adds a command line option to select a better mapping from
midi controller values to dB sliders. The default stays as a linear
mapping, which has the disadvantage, that a sensible area to adjust your
volume (which ist mostly in the range of 0..-12dB) is in the upper
1/10th of your midi controller. This patch adds a map, which consists of
two linear functions, so that the upper half of your midi controller
controls values from 0..-12dB, the lower half then controls -13..-96dB.