Added keyword to handle missing flags when reading DataQualityDict
This PR does two things:
- added
on_missing='error'keyword forDataQualityDict.read, to handle user-supplied names that are not found, - renamed
flag->nameandflags->nameskeywords forDataQualityFlag.readandDataQualityDict.readrespectively (with deprecationwarnings)
This patch is mainly to fix the issue of reading a list of flag names from multiple files when not all flags exist in every file, but are split across the list.
cc: @lauranuttall