-[FEATURE] Support for updating fields on duplicate key in bulk update (mysql only) [#2692](https://github.com/sequelize/sequelize/pull/2692)
-[FEATURE] Basic support for Microsoft SQL Server
-[INTERNALS] Deprecate migration logic. This is now implemented in [umzug](https://github.com/sequelize/umzug) and the [CLI](https://github.com/sequelize/cli).
-[BUG] Fixed various inconsistencies with `Instance.update` and how it behaves together with `create`, `fields` and more.
#### Backwards compatability changes
- Some of the string error messages for connection errors have been replaced with actual error instances. Checking for connection errors should now be more consistent.
