Moderninze the code
BUG_FIX:  was always returning nan for single spectra.
Automatic style corrections courtesy of autopep8.

Add test to detect the bug.
Warn the user when no inflexion point is found in range.
Automatic style corrections courtesy of autopep8.
Improve docstring.
Automatic style corrections courtesy of autopep8.
BUG_FIX: fourier_ratio_deconvolution broken for single spectrum.
Merge branch 'BUG_FIX_estimate_elastic_scattering_threshold' into 0.7.1
Merge branch 'BUG_FIX_fourier_ratio_single_spectrum' into 0.7.1