feature/masses_data_loader

@dismorfo Do you want to offer the ability to pass in a non number argument? It sounds like you want to throw an `ArgumentError` instead of defaulting to 0 for non numeric. If you want to default when no argument is passed in you can say something like the following:

```ruby
unless start.present? && !is_numeric?(start)
  throw ArgumentError("Expecting start to be a number")
end
```

Then you can set start below that:

```ruby
@start = start || 0
```

Similarly for `@rows`