= New Features

* An instance_specific_default plugin has been added for setting the
  default for the :instance_specific association option, or
  warning/raises in cases where it is not specified.  This allows
  you to easily find associations that would be considering instance
  specific by default, and mark them as not instance specific for
  better performance.

= Other Improvements

* Setting the :instance_specific association option to false now
  works correctly if the association uses a block.  Associations
  that set the :dataset option are now always considered instance
  specific, even if the :instance_specific option is explicitly
  passed.

* The validation_class_methods plugin now considers all :if,
  :allow_missing, :allow_nil, and :allow_blank options.  Previously,
  it only considered the first of those options that was set.

* Model.finalize_associations no longer breaks if you have
  instance-specific associations.

* Model.plugin now warns if you load the plugin with arguments or a
  block if the plugin does not accept arguments or block.  This is
  because a future change to Sequel could break the call.

* When emulating unsupported alter table operations on SQLite, Sequel
  now copies composite unique constraints unless the alter table
  operation is the dropping of a unique constraint.

* Sequel now recognizes an additional disconnect error in the oracle
  adapter.

* In the run_transaction_hooks extension, calling
  run_after_{commit,rollback}_hooks now raises the correct exception
  class.

* In the pg_range extension, conversion procs for the tsrange[] and
  tstzrange[] types are not added unless the Database uses the
  pg_array extension.

* Multiple unnecessary conditionals in plugins and extensions have
  been removed.

* Sequel plugin and extension code now have 100% branch coverage.

* Sequel now avoids a statement not reached verbose warning in
  Dataset#clone.

= Backwards Compatibility

* The output of Dataset#to_dot in the to_dot extension has changed
  slightly, including hash entries with nil keys.  These entries
  were previously ignored.
