Compare items between job

[manycoding]

As per https://github.com/scrapinghub/arche/pull/167#issuecomment-533210953

res.show()
>>>55 items hasn't changed
800 items were added
200 items changed

res.additional_stats.added
>>>key column_x ... column_f
...
res.additional_stats.changed
key column_x_left column_x_right
...