PCM interpolation

YM2612 did not have internal interpolation for samples Thus, all PCM sounds not sampled at 55kHz have distortion due to spectrum duplication. This version adds a fixed x2 rate scaler for PCM samples using a CIC filter (second order, M=4). The results are very nice with much clearer samples. Bass might be too strong. I may consider compensating for bass and adding automatic sample rate detection to vary the interpolation filter rate on later releases.