Add support for parallel requests about apai-io

[Exeu]

This feature does not make sense with the amazon api since the requestes which could be done are strictly limited by amazon. Between each Request you are going to do you have to wait at least one second before you can do the next one.
Fireing multiple requests at the same time does not make sense here because only one of these requests will succeed.

[troxler]

This is not entirely true. According to Amazon your maximum number of requests per second firstly depends on your partnership performance. And secondly, you also have some allowance for bursty traffic. Both cases result in more requests per second. By measuring, I also cannot confirm the strict limit. Two consecutive API requests using the same partner ID often successfully obtain data in under one second of total running time. And this has nothing to do with the number of my sales.