Following the discussion about an API to pin and unpin preset samples in the sample cache here:
https://lists.nongnu.org/archive/html/fluid-dev/2020-10/msg00016.html
Short explanation of the change:
Only the default loader currently supports dynamic sample loading, so I thought it might be a good idea to keep the changes for this feature mostly contained in the default loader as well. I've added two new preset notify flags (FLUID_PRESET_PIN and FLUID_PRESET_UNPIN) that are handled by the preset->notify callback and trigger the loading and possibly unloading of the samples.
