Describe the feature request

In poll_for_updates, errors are consumed and a fixed log message is printed instead. For example, if the HTTP request fails it simply prints warn!("poll: failed to retrieve features"). This is unhelpful for debugging. It'd be helpful to print the particulars of the error.

Background

I am currently attempting to use unleash-api-client in a cloud-hosted project. It has started sporadically failing, but without information on the particulars I can't easily debug it.

Solution suggestions

It'd be a case-by-case basis, but generally would just need to include a debug-formatted version of the originating error.