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Added features and modifications:
- Modified readcoord.readcif to accept a `phaseblock` argument, to allow better reading of multi-phase CIF files.
- Tests are now controlled by pytest, rather than unittest
- Added update-check to CIFellipsoid and EllipsoidGUI to check for newer versions of PIEFACE.
Bug fixes:
- Changed readcoords.readcif so that if neither of `_symmetry_Int_Tables_number` or `_space_group_IT_number` is present, spacegroup
is set to None. Does not currently affect any other routine in pieface.
- Minor updates to documentation and code organisation
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