Allow ignoring of specific columns

[pserra]

Problem

Currently there is no good way to exclude specific fields from the match process. When you're comparing two versions of a report, one with a new column and the original, you may want to check whether the reports are otherwise identical, as to ensure there were no other side-effects as a result of adding the column.

Examples:

1. You're looking to compare two CSVs based on only a few fields.
2. You're comparing two CSVs with different, but important id columns.
3. One CSV has a sum or total fields that the other does not.