Promote DigitalPhaseLockedLoop to a template, simplify to O(1) add_pulse.

Storage/Disk/Track/TrackSerialiser.cpp

@@ -14,18 +14,18 @@
 // just return a copy of that segment.
 Storage::Disk::PCMSegment Storage::Disk::track_serialisation(const Track &track, Time length_of_a_bit) {
 	unsigned int history_size = 16;
-	DigitalPhaseLockedLoop pll(100, history_size);
 	std::unique_ptr<Track> track_copy(track.clone());
 
 	// ResultAccumulator exists to append whatever comes out of the PLL to
 	// its PCMSegment.
-	struct ResultAccumulator: public DigitalPhaseLockedLoop::Delegate {
+	struct ResultAccumulator {
 		PCMSegment result;
 		void digital_phase_locked_loop_output_bit(int value) {
 			result.data.push_back(!!value);
 		}
 	} result_accumulator;
 	result_accumulator.result.length_of_a_bit = length_of_a_bit;
+	DigitalPhaseLockedLoop<ResultAccumulator> pll(100);
 
 	// Obtain a length multiplier which is 100 times the reciprocal
 	// of the expected bit length. So a perfect bit length from