Move exceptions into a sub-namespace #18
Description
Something I neglected in 1.1.0 is to ensure that users have a decent experience when trying to discover Cursively's API through IntelliSense or the online API browser.
At the moment, all the new exception types added for the header-aware visitor simply live in the top-level "Cursively" namespace, which makes it harder to find the small handful of types that are meant to serve as starting points for the API.
Moving these to a Cursively.Exceptions namespace should help with this.
This would be a source and binary breaking change.