libaes_siv release candidate

[Daniel Franke]

The current HEAD of libaes_siv is a release candidate. Whether or not
it becomes the release depends on what I decide to do about the CentOS
6 issue, which in turn depends on the OpenSSL team getting back to me.
I'm also waiting on Hal to run it through his build farm again to let
me know if last-minute changes caused any breakage. If the answers
turn out to be "nothing" and "no", then this will become 1.0.1. For
the meantime, I've tagged HEAD with '1.latest' which is what the CI
system can use to get something of suitable stability for testing. If
I make any further changes before 1.0.1, I'll re-point the tag.