Adding db.ID interface.
PrimaryKeys in schema is now an array of strings.
PostgreSQL: Adding support for composite keys while keeping backwards compatibility with single numerical IDs.
Adding interface Constraint{}.
PostgreSQL: Adding Constraint() interface.
Changing interface names to IDSetter and Contrainer, for consistency.
Let Table now accepts Raw as value.
PostgreSQL: Using composite keys instead of non-numeric keys for clarity.
MySQL: Adding support for composite keys.
SQLite: Adding support for composite keys.
QL: Adding support for db.Constrainer and db.IDSetter interfaces.
MongoDB: Adding support for db.Constrainer and db.IDSetter.
IDSetter will expect a map instead of an array to make code consistent and
easier to refactor. Testing this approach with the PostgreSQL adapter.
MySQL: Upgrading IDSetter interface.
PostgreSQL: Removing superfluous snippet.
SQLite: Upgrading IDSetter interface.
MySQL: Fixing SetID() setter in test.
Updating SetID() declaration in tests.
SQLite: Don't attempt to allocate a new slice if we don't need it.