Initial implementation.

Add `lib/connector.js` and `lib/sql.js` from
strongloop/loopback-datasource-juggler@5937f0c.

Export both classes from `index.js`

Rename `BaseSQL` to `SqlConnector`.

Fix jshint errors.
fixup: add a stub test
Merge pull request #2 from strongloop/feature/refactor-connector-base

Initial implementation.