Add Multiple Emails to Recipient Lists

Really simple addition to support adding multiple email recipients to a list.

I was able to get it to work previously with:

```ruby
list_emails_obj.add list: "Test 1", data: [{email: "test1@sparkart.com", name: "test1"}.to_json, {email: "test2@sparkart.com", name: "test2"}.to_json, {email: "test3@sparkart.com", name: "test3"}.to_json]
```

These changes make it so that I don't need to add `.to_json` to every element of the array:

```ruby
list_emails_obj.add list: "Test 1", data: [{email: "test1@sparkart.com", name: "test1"}git , {email: "test2@sparkart.com", name: "test2"}, {email: "test3@sparkart.com", name: "test3"}]
```