Glad to see there's been progress on this front! The lack of E2E encryption is literally the last thing holding me back from building apps with Matrix. Can't wait to give it a try! =)
Axolotl has a well defined message structure using established crypto functions. All of them, for example, except Curve25519 are in Crypto++. You can probably fairly easily bake your own, albeit I'd use the olm from Matrix and just make theirs work well first.
