= New Features

* Model#column_previously_was and #column_previously_changed? have
  been added to the dirty plugin, for getting the previous values
  of the column before saving and for whether there were changes
  before saving.
  
  Model#column_previously_changed? accepts :from and :to options
  to allow you to more easily determine if the value changed from
  and/or to specific values.

  This information was previously obtainable via
  Model#previous_changes, but these new methods offer a friendlier
  interface.

* Postgres::PGRow::{Array,Hash}Row#op has been added to the
  pg_row_ops extension if the pg_row extension is loaded.  This
  is similar to how the pg_array_ops, pg_hstore_ops, and
  pg_json_ops and #op method to their objects.  This makes it
  easier to perform row operations on literal rows.

= Other Improvements

* The schema_dumper extension now supports more unsigned numeric
  types, such as "decimal(7,2) unsigned" and "real unsigned".

* IntegerMigrator now raises an Migrator::Error if attempting to
  migrate down when there are migration files missing and needed for
  the down migration.  Previously, IntegerMigrator would not raise an
  exception and would make no database changes in this case.