Description:
    The extension_migration generator creates a stub for a new migration for an 
    extension.

    The generator takes the extension name, a migration name as its arguments,
    and an optional list of attribute pairs as arguments. The migration name 
    may be given in CamelCase or under_score.

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

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

Examples:
    `./script/generate extension_migration MyExt AddSslFlag`

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

    `./script/generate migration MyExt AddTitleBodyToPost title:string body:text published:boolean`
    
    This will create the AddTitleBodyToPost in vendor/extensions/my_ext/db/migrate/20080514090912_add_title_body_to_post.rb
    with this in the Up migration:

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

    And this in the Down migration:
    
      remove_column :posts, :published  
      remove_column :posts, :body  
      remove_column :posts, :title
