jeremyevans/sequel — pull request #658 by ujifgc (2013-05-13 08:54:18+00:00)
Title: Add automatic migration mechanism.

Usage:
```ruby
DB.upgrade_table? :accounts do
primary_key :id
column :title, String, :default => 'foobar'
end
class Account < Sequel::Model
end
```

The :accounts table will be created if it does not exist. If it exists and lacks :id or :key column, the corresponding column will be added with ALTER TABLE. If the table already has the column, no action will be performed on it.