Description:
    The railmail table migration generator creates a migration for adding the railmail_deliveries table 
    used by Railmail.

    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 railmail_migration AddRailmailTable

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