New release

New features and bug fixes. See changes.txt for details.

TYPES:

1. Check lower case only for method in CorrData.stack()
2. Bugs and improvements in DvvData and CorrData to save large attribute to asdf
3. Added psd() method in CorrData to plot psd of the CorrData result.
4. Added plot() method in FFTData to plot the amplitude spectrum of the FFT results.
5. Improved plot() for DvvData with smoothing option.
6. Minor bug fixes and improvement for FFTData in merging and plotting.

DOWNLOADERS:

1. Use inventory to remove response in read_data for miniseed
2. Added ms2asdf() to convert miniseed files to asdf files.

NOISE:

1. Optimize memory usage for merge_chunks()

PLOTTING:

1. Added plot_psd() to plot the psd of an array (works with 1-d and 2-d array only for now.)
2. Updated plot_eventsequence() to have the option of plotting depth as the ydata.

UTILS:

1. Minor bug fixes in read_gmtlines()
2. Added psd() to get the power spectral density of an array