Raise error if batch command partially failed

[BRMatt]

Operations such as lists.batch_subscribe return errors in an errors array, rather than a single error value that the response handler expects. At the moment if an error occurs during that operation gibbon silently returns.

As we can't raise individual errors for each error in the array we have two choices:

1. Raise a Gibbon::MailChimpError for the first error in the array
2. Introduce a new Gibbon::MultipleMailChimpErrors to encapsulate all of the errors

Thoughts?

[amro]

The trouble with raising an error in batch cases is the caller wouldn't have the information to handle the successful portion of the response. This makes building apps that sync lists with MailChimp tough. And I don't believe the successful portion of the response belongs in the error.

Would raising an error if all of the batched items fail be helpful?