Tomni

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- BUGFIX: Bufferoverflow make_mask_ellipse (again/still)
remove times 2 for all values in the function

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- add ellipse to json2mask
- BUGFIX: Bufferoverflow make_mask_ellipse
- BUGFIX: Make make_mask_ellipse accept floats

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- add mask2bbox
- add contour2bbox
- add check_overlap_bbox

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- add mask2json
- add json2mask

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Upgrade/change requirements to work with python 3.9
Opencv needed fuzzy requirments
Remove scikit-image from requirements by replacing the function with numpy function

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speedup positions2contour by replacing for-loop with numpy slicing