Subscribe to list different from app.config list

Add the ability to subscribe to a list different from the list ID in the
app.config file

Hi, thanks for the library you wrote, I have been using it and has been of great help.

I have added a small piece of functionality. Basically the change allows the developer to specify a list ID other than the list ID in the configuration. I have left the existing functionality in place and all the tests pass (after updating the app.config for my MailChimp setup).

Thanks
Pieter