Description:
    The migration generator creates a stub for a new database migration.

    The generator takes a migration name as its argument.  The migration name may be
    given in CamelCase or under_score.

    The generator creates a migration class in db/migrate prefixed by its number
    in the queue.

Example:
    ./script/generate migration AddSslFlag

    With 4 existing migrations, this will create an AddSslFlag migration in the
    file db/migrate/005_add_ssl_flag.rb