Add TODO for analyze peak optimization

analyze_peak.cpp

 	max = max_sample;
 	do {
 		int16_t d=*p++;
+		// TODO: can we speed this up with SSUB16 and SEL
+		// http://www.m4-unleashed.com/parallel-comparison/
 		if (d<min) min=d;
 		if (d>max) max=d;
 	} while (p < end);