Bug in FrequencySeries.interpolate

Created by: alurban

The method FrequencySeries.interpolate() is currently always setting its output f0 to 0 Hz. This causes problems if the original FrequencySeries begins above 0 Hz, as the interpolated FrequencySeries will start at 0 Hz but have the same bandwidth as the original, so its first several samples will be zero.

To fix this, the output FrequencySeries should (1) interpolate in the correct frequency range and (2) inherit the f0 attribute from the original FrequencySeries.