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 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