------------------
New features
* st_var can now be array-like. The array-like can vary in x or time, or both.
* When converting from a xr.Dataset to a DataStore object, the attributes arenow transfered over
* Added 'verbose' kwarg to shift_double_ended utility function to silence theconsole output
Bug fixes
* If the '_sections' attribute is missing from a DataStore object it is automagically re-added.
* Assert that stokes variances are passed when running a double-ended WLS calibration
* Added check for NaN/inf values in wls_sparse solver to avoid unclear error messages
* Before calibration, the values of the used reference temperatures are checked if they are valid (float dtype, no NaN/inf values, correct time dimension)
Others
* European Geosciences Union conference 2020 presentation added
* Updated documentation with content article
* Use YAPF formatting of the Python files
* Travis-CI.org integration in GitHub restored.