callers of the encode interface are now required to pass in the correct iv for
the ciphertext being encoded

instead of confusing it with the segment length sometimes, which includes
padding bytes

It doesn't have an assert but it prints the wrong output

need to move the key stuff to a new branch and finish it on its own probably

Lots of fields left incorrectly populated but at least the erasure encoding is
working so we can probably read (without verification) real shares now.