lei_to_mail: start --augment, dedupe, bz2 and xz

lei_to_mail: start --augment, dedupe, bz2 and xz

--augment will match the mairix(1) option of the same
name to augment existing search results.  We'll need
to implement deduplication for a better user experience.

mutt ships with compressed mbox support for bz2 and xz,
at least, so we'll support those out-of-the-box.