Invoke wraps a function which may fail with an error to match the Invoker interface. Use it to supply functions matching this signature to AppendInvok

RemoveAll is a multierr.Invoker that deletes the provided directory and all of its contents.

Invoker is an operation that may fail with an error. Use it with AppendInvoke to append the result of calling the function into an error. This allows

multiError is an error that holds one or more errors. An instance of this is guaranteed to be non-empty and flattened. That is, none of the errors in

richFormatError is an error that prints a different output depending on whether %v or %+v was used.