BUG_FIX: two_area_background_estimation was raising an exception when not PowerLaw component in model.
Automatic style corrections courtesy of autopep8.
New EELSModel._get_first_ionization_edge_energy method.
Automatic style corrections courtesy of autopep8.
Simply PowerLaw.estimate_parameters code and add test for only_current=False
Automatic style corrections courtesy of autopep8.
Automatic style corrections courtesy of autopep8.
Make EELSModel.fit_background more readable and add tests.

The "kind" argument was replaced by "only_current" keeping the same
functionality and default. Tests added. The code was simplified to enhance
readability. A bug that was raising an exception when a background component
that was not a powerlaw was present has been fixed.
Automatic style corrections courtesy of autopep8.
Merge pull request #321 from francisco-dlp/ENH_eelsmodel_background

Enh eelsmodel background