API Changes

• moved gridder from recip.py -> core.py
• Changes
• Changes
• moved fit_quad_to_peak from spectroscopy.py -> fitting/__init__.py
• Changes
• Changes
• Changes
• Renamed detector2D_to_1D to img_to_relative_xyi
• Change API of img_to_relative_xyi
• significant changes to the fitting package
• Change return tuple on linear_spectrum_fitting function
• Grid-building functions
• Image Processing: Arithmetic changes
• nnls_fit functions
• Moved extract_label_indices function from correlation.py to roi.py
• Moved extract_label_indices function from correlation.py to roi.py
• Changes to circular_average function
• Changes to bin_1D function