Release 0.6.16

[ENH] Minimum Noise Fraction denoising preprocessor
[ENH] Shift and scale preprocessor
[ENH] Preprocess Spectra: supports categories of preprocessors
[ENH] File reader for 4D mapping stacks from the SGM beamline at CLS
[FIX] Fixes for Peak Fitting (support newer lmfit)
[MNT] Refactor preprocess tests