Throw Clearbit Exceptions instead of Nestful

[harlow]

We should wrap the Nestful errors with Clearbit exceptions. Users of the Clearbit gem shouldn't need to know about the Nestful gem.

[maccman]

👍

[swanandp]

👍 this would be very useful.

[xtina-starr]

This would be really nice! This plus documentation of why and what kinds of emails are deemed invalid would be 💯! I found myself creating a rescue for Nestful::ResourceInvalid and it just felt really odd seeing that it was clearly a Clearbit thing.