* Fix a bug in ma_gainer where smoothing isn't applied correctly thus resulting in glitching.
* Add support for smoothing volume changes of sounds with `ma_sound_set_volume()`.
* Add support for volume smoothing to sounds when changing the volume with `ma_sound_set_volume()`. To use this, you must configure it via the `volumeSmoothTimeInPCMFrames` member of ma_sound_config and use `ma_sound_init_ex()` to initialize your sound. Smoothing is disabled by default.
