Using exponential decay for filter envelope release
Using exponential decay for filter envelope release

Instead of a linear decay. This matches the changes made to the
gain envelope release in 1c31ec4284030fcd3d848653423ec619ed1eb97b.

In particular, this makes the filter sweep during the release
portion of a filter envelope sound more noticeable, and general
better overall.

jstrait/jssynth,jstrait/jssynth