Duplicates are confusing

[manycoding]

At the moment, we have 3 rules which do more or less the same, i.e. find duplicate items by column/columns:
https://github.com/scrapinghub/arche/blob/master/src/arche/rules/duplicates.py
find_by (multiple columns support, "Duplicates")
find_by_unique (one field, "Uniqueness/Duplicates By unique Tag")
find_by_name_url (tags, named "Duplicated Items/Duplicates By name_field, product_url_field Tags")

That's confusing. As a part of #123 , I propose to move from tags to arguments which basically removes the need of using tags and obsoletes the last two.

Arche(uniques=["url", ("id", "color")])
single entry url will check that the column contains only unique values
tuple ("id", "color") will check that all rows contain unique combination of id color
@peonone