Story: Update Rows

[flyingzumwalt]

Scenario:

1. Import a dataset
2. Modify some rows in the source dataset
3. Import the changes into dat

This depends on #12 because in order to update rows in a dataset you need to specify the key column. Read the discussion in #15, which has a big impact on how we implement this feature.

If a key was provided to the import command, we need to look in the index for a row with that key.

• if the row doesn't exist, write a new row to the feed (create row)
• If the row already exists and hasn't changed, do nothing.
• If the row already exists and the new values are different, write an update to the feed (update row)

[flyingzumwalt]

Rebooting issues (taking a different approach to roadmap)