Public API methods to throw errors?

[feodormak]

Is your feature request related to a problem? Please describe.
The public APIs for this framework currently does not return any errors, just .available or .none on completion. checkForUpdates returns .none if there is no or poor connectivity.

Describe the solution you'd like
The method checkForUpdates should have a completion handler of @escaping (UpdatesResult, Error) -> Void to allows context as to why there is currently no update, and allow us to choose how to present the info in-app.