* Introduce file system abstraction and an S3 implementation
* Support arbitrary absolute paths and delegate resolution to file system
* Remove accidental notebook file
* Apply suggestions from code review
Co-authored-by: José Valim <jose.valim@dashbit.co>
* Apply review comments
* Add missing path assertions
* Apply review comments
* Fix test saving notebook in project root
Co-authored-by: José Valim <jose.valim@dashbit.co>
