Add transposed_table_for to render a collection in columns

A new component to render records in table columns rather than table rows. The image shows the difference between the two components.

![transposed_table_for](https://f.cloud.github.com/assets/25094/1276013/432adbe2-2e25-11e3-867e-2582c8c3b95b.png)

```ruby
transposed_table_for CostType.all do
  column :name
  column :id
  column :created_at
end

table_for CostType.all do
  column :name
  column :id
  column :created_at
end
```

I considered using a `row` call, but thought it would be nice to have the exact same API as `table_for` for portability. Thoughts?