Stereo chorus

I noticed that fluidlite is using an older, mono implementation of the chorus effect:

Lines 482 to 484 in 7c150b0

    
           /* Add the chorus sum d_out to output */ 
        
           left_out[sample_index] += d_out; 
        
           right_out[sample_index] += d_out;

It would be nice to update this to the latest upstream chorus implementation, which is stereo:
https://github.com/FluidSynth/fluidsynth/blob/master/src/rvoice/fluid_chorus.c

In my opinion, poor chorus implementations have been a major sore spot of General MIDI over the years. (In my project, I had chorus completely disabled for a long time.) It could really sound like a rich Juno 106 chorus for little to no extra cost.

	/* Add the chorus sum d_out to output */
	left_out[sample_index] += d_out;
	right_out[sample_index] += d_out;