Introduce a mailchimp service, and expose API exceptions to service users.

Background

I'm trying to use mailchimp module as part of another module that would programmatically subscribe a user to a given list and do more stuff based on the subscription result (including different possible API errors) ...

Problem

mailchimp_subscribe_process is kind of "swallowing" the exception (which is understandable, because it could run with cron, and it's not appropriate to throw exception during cron run), but this is also making the use of this module as an API rather hard, because we don't know what exception had happened in case of an exception.

Proposal

introduce a service that can be used by other modules (including mailchimp_subscribe_process) that throws proper exceptions, and then catch those exceptions as you would normally do in mailchimp_subscribe_process