Description:
    Stubs out a new database migration. Pass the migration name, either
    CamelCased or under_scored, and an optional list of attribute pairs as arguments.

    A migration class is generated in db/migrate prefixed by a timestamp of the current date and time.

    You can name your migration in either of these formats to generate add/remove
    column lines from supplied attributes: AddColumnsToTable or RemoveColumnsFromTable

Example:
    `rails generate migration AddSslFlag`

    If the current date is May 14, 2008 and the current time 09:09:12, this creates the AddSslFlag migration
    db/migrate/20080514090912_add_ssl_flag.rb

    `rails generate migration AddTitleBodyToPost title:string body:text published:boolean`

    This will create the AddTitleBodyToPost in db/migrate/20080514090912_add_title_body_to_post.rb with this in the Change migration:

      add_column :posts, :title, :string
      add_column :posts, :body, :text
      add_column :posts, :published, :boolean

Migration names containing JoinTable will generate join tables for use with
has_and_belongs_to_many associations.

Example:
    `rails g migration CreateMediaJoinTable artists musics:uniq`

    will create the migration

    create_join_table :artists, :musics do |t|
      # t.index [:artist_id, :music_id]
      t.index [:music_id, :artist_id], unique: true
    end
