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Changes
- raise new fitsio.FITSFormatError exception when we detect format
errors in a FITS file. Currently this only raises when extensions
are not properly marked with XTENSION but we can expand this over time
Bug Fixes
- Bug not writing compression qlevel when it is set to None/0.0
This was preventing lossless gzip compression
- work around cfitsio bug when creating HDU for lossless gzip compression,
reopen file instead of just an update hdu list