Allow designation of "key" columns during Table Comparison

[Brandon-Champion-KT]

I frequently need to compare CSVs with columns such as Part Number and Description. Part Numbers can be very similar to one another, which may be detected as a change. An example would be in one file, there could be Part Number "ABC-123" and the other file contains "ABC-111". WinMerge may detect this as a change rather than a distinctly different line. It would be useful to be able to designate columns such as this as "key" columns, meaning WinMerge should only match lines if key values are identical.