New features and improvements

This release added new features, fixed bugs, and improved some functionalities. See changes.txt for details. Here is a list of key changes in this version.

Updates in v0.7.5
NOISE:

1. correlate(): discarded lines removing peak at zero lag (demean of the spectrum).

MONITORING:

1. get_dvv: improved plot saving. Fixed a bug where stack_method was not specified for substacking.
2. ts_dvv: trimed data to only compare the original data window, excluding the padded zeros.
3. xc_dvv: newly added method using moving window cross-correlations. needs improvements and more tests.

DISPERSION:

1. get_dispersion_image: use adaptive window size for different periods, increasing with periods.
   This is options. Options to specify minimum number of trace and minimum number of wavelength.

• added option to specify energy type, "power_sum" or "envelope".
• added plotting options.
• fixed bugs when only processing one side.

2. renamed get_dispersion_waveforms() to narrowband_waveforms to avoid using the word "dispersion".

DOWNLOADERS:

1. read_data(): minor bug fixes.
2. get_data() and get_sta_list(): added flexibility of specifying the source, which could be a Client object.
3. download(): added verbose to calling getdata().

STACKING:

1. Added handling of small data size, i.e., 1 trace, which will return the data without stacking.
2. Added option of using DOST for tfpws, based on the implementation by Jared Bryan. It was added as a new function:tfpws_dost.

UTILS:

1. Added two functions to get image gradient and convert xyz to matrix, without interpolation.
2. extract_waveform: read all data if not specifying stations.

PLOTTING:

1. Added facecolor to set the background of plots to white.
2. Added plot_dispersion_image() to plot dispersion image.

SIMULATION:

1. New module for seismic wave simulations.