dbuscombe-usgs/pyDGS: version 4.0

First significant update since 2016

• switched to using the pywavelets package (see here) for wavelet calculations, which removes many issues with my previous cython translation, including no need to specify parameters
• more test data
• improved image filtering, which now occurs as standard
• improved test script to provide example usage
• simpler to install. no code compilation, no pip support, no setup.py script