Xypattern

- adding and subtracting patterns with different x-values will now work both with linear interpolation (before subtraction was using cubic interpolation and adding linear)
- pattern to_dict and from_dict now also save and restore auto_bkg and auto_bkg_roi
- added a copy method to pattern class
- pattern changed signal now passes the pattern itself as argument
- improved code documentation and added examples
- added online documentation at https://xypattern.readthedocs.io/en/latest/

- now correctly saves a file without background (subtract_background parameter false) when auto_bkg is set

- fixed inclusion of compiled smooth bruckner functions in wheels on linux and macos

- added feature to delete a range in a pattern
- added filename field in pattern, which contains complete filepath (name will still just hold the name)
- added transform_x function to modify the x-axis in place (will also update backgrounds)
- changed the auto background api, new usage:

python
pattern.auto_bkg = SmoothBrucknerBackground()
pattern.auto_bkg_roi = [10, 20]
pattern.auto_bkg = None will switch it off

- enable poetry versioning plugin during build, to hopefully work when installing with pypi

- fix constraints to also actually work with python 3.8