Add migration to convert title and subtitle to "text" fields from varchar(255).
user
```ruby
class MakeDocumentsTitleAndSubtitleText < ActiveRecord::Migration
  def self.up
    change_column :documents, :title, :text
    change_column :documents, :subtitle, :text
  end

  def self.down
    raise ActiveRecord::IrreversibleMigration
  end
end
```
assistant