Niondata

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- Fixed RGB issues when data backed by h5py array instead of numpy array.
- Changed rescale to take a new parameter 'in_range'.
- Changed rgba/rgb functions to clip data to 0, 255.
- Split display functions into element and scalar functions.

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- Introduce calibrated coordinates and reference frames (preliminary).
- Improve handling of NaNs in rebin_1d.
- Add xdata function rebin_image.
- Fix issue with bounds when rotating data.
- Fix issues with concatenate and data descriptor.
- Add xdata functions to split/join sequences.
- Add template matching functions to xdata.
- Make pick functions work for sequences of spectrum images.

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- Change shift/align functions to use spline-1st-order; add Fourier variants as alternative.
- Fix calibration bug in xdata concatenate (and some cases of hstack, vstack).
- Add function to generate elliptical masks.
- Change FFT to put calibration origin at 0.5, 0.5 pixels from center.

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- Improve handling of squeeze/calibration for sequence measurements.
- Add new navigation properties (combo of is_sequence and collection) to data.
- Support slicing on RGB sequences (for display data).

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- Added optional registration area bounds to align and register functions.

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- Added mean function. Add keepdim param to mean/sum. Allow negative indices.