Description:
    Generates a migration of database content.

    To import database content from a json file move your json file to db/migrate_cards/data
    and choose as migration name import_<filename>.

Example:
    <%= banner_command %> generate card:migration better_commented_search_cards

    This will create:

        db/migrate_cards/(migration_number)_better_commented_search_cards.rb

    ...which is set up to use methods in lib/card/migration.rb


    <%= banner_command %> generate card:migration import_better_search_cards

    This will create:

        db/migrate_cards/(migration_number)_import_better_search_cards.rb

    ...which is set up to import data from db/migrate_cards/data/better_search_cards.json