Remove chai #250
Description
Before we consider bundling lab with a new assertion library, we should remove the existing one. Once we do that, adding a new built-in will be a minor release. By removing it, we ensure a smoother transition as any replacement will include many breaking changes (e.g. no longer using properties for assertsion .exist turns into .exist()).
We should also remove all the custom handling for chai in the reporters. Any such cleanup should happen in the assertion library itself.