Preserve relationships between emails and attachments.

[DavidCaliri]

It seems that if you extract the attachments with the -a flag there is no way of knowing which attachments are from which emails. It would be nice if the generated json or csv recorded the attachment name at least. It would also be great if the attachment had recorded in its metadata a reference to the email from which it came. You could also include in the metadata program credit for that matter like, "Extracted using mbox-to-json v1.0.5."

[PS1607]

This is a good suggestion. I'll work on this