SQL sync first cut

[oscarbatori]

WIP still, but tests suite is green.

To do:

• [ ] implement for Postgres
• [ ] get Dolt diff based features working
• [ ] sort out Doltpy management of connections
• [ ] RDBMS to Dolt sync
• [ ] docs

I reckon these will be relatively straight forward to get something basic working since the test harness is now setup.

[oscarbatori]

I ended up having to make a fair number of updates to this, including:

• implementing updates and deletes for when Dolt repo has had update or delete operations applied
• removing Postgres support as I need to do a bit more work on getting updates and deletes working
• fix some miscellaneous issues in Doltpy, most importantly the feature of sitting on connection objects, instead clients should request a connection object