Regressions

• [Ecto.UUID] Remove UUID version validation as it is not part of the RFC
• [Ecto.Adapters.Postgres] No longer add parens to migration index expression in order to support NULL/ASC/DESC

Enhancements

• [Ecto.Changeset] Add unsafe_validate_unique/3 which validates uniqueness for faster feedback cycles but without data-integrity guarantees
• [Ecto.Query] Support aggregations in type/2 in select
• [Ecto.Schema] Support @field_source_mapper in Ecto.Schema as a mechanism to programatically set the :source option