add CFB8 support for AES/3DES on CommonCrypto and OpenSSL backends
add some docs and changelog
native_size is not needed with the CFB8 approach we chose
sometimes you can't read and leave things in
Merge pull request #1043 from reaperhulk/support-some-cfb8

add CFB8 support for AES/3DES on CommonCrypto and OpenSSL backends