Feature to enable table row transformations

This enables table row transformations.

Typical use case for a table transformation:
 ```php
      /**
     * @transform table:username,age
     */
    public function transformShowsTable(TableNode $table)
    {
        $users = [];
        foreach ($table as $row) {
            $users[] = new User($row['username'], $row['age'];
        }
        return $users;
    }
```

The loop is pretty boilerplate, so this PR enables the following:

```php
     /**
     * @transform table_row:username,age
     */
    public function transformShowsTable(array $row)
    {
        return new User($row['username'], $row['age'];
    }
```