Broken again

Just want to commit before I change anything else.

Trying to get it so you can insert/extract multiple times w/ the same
key/nonce. i.e. A signature "file" that points to a content file: two
hashtrees, then both encrypted to a third "file" with the key/nonce/etc.
Signature should have level = top of content's level + 1. Third file
isn't encrypted, but has encrypted data w/ nonce (0,0).