cc @taigrr
This PR will _hopefully_ help to fix some critical isseus in the real world with several or more [Yarn.social](https://yarn.social) pods running [yarnd](https://git.mills.io/yarnsocial/yarn) where starting back up after a power failure or crash can sometimes result in an empty `config.json` or empty `meta.json` or both!
I'm not actually sure how this can arise, and as yet I haven't been able to reproduce it (_I can only assume this has to be failures cases outside of our control_); but in any case the application and database is recoverable by simply `rm config.json` and/or `rm meta.json`.
So this PR makes errors loading the config and metadata first-class errors and exported error types that consumers of the library can use to perform automated recovery without requiring human intervention.
Basiclaly in this case it's no big deal we lost the database config of metadata, we can simply carry on.
Co-authored-by: James Mills <prologic@shortcircuit.net.au>
Reviewed-on: https://git.mills.io/prologic/bitcask/pulls/241
Co-authored-by: James Mills <james@mills.io>
Co-committed-by: James Mills <james@mills.io>
