New feature and improvements

v0.7.4 contains new features and improvements with bug fixes. See changes.txt for details (as summarized here).

Updates in v0.7.4
UTILS:

1. Added spectral whitening function: whiten(), for time series data.

MONITORING:

1. Added whitening option in get_dvv().

TYPES:

1. FFTData, fixed a minor bug when getting Nfft for single trace data.
2. CorrData shaping: trim_end option to accommodate the need by FWANT.

PLOTTING:

1. plot_psd() bug fixed

STACKING:

1. Fixed a bug in robust stacking when the trace amplitudes are anomalously small.

DOWNLOADERS:

1. ms2asdf(): added option to specify response file.

DISPERSION:

1. get_dispersion_waveforms: Use period to get the evenly-spaced period vector.
2. get_dispersion_image: new function to extract dispersion image in velocity-period domain/space.