1. ChaCha20, two-key 3DES and DES-X encrypted OpenSSL PEM files
2. AES-GCM and Chacha20+Poly1305 encrypted SSH keys
* OpenSSH uses a slightly different algorithm for its
`chacha20-poly1305@openssh.com` than defined in the RFC.
Therefore add an `openssh_compat` flag to
`chacha20poly1305_state`.
* Add the option to give a 16byte IV and no counter, when calling
`chacha20poly1305_memory()`
* Add support for DES-X
Signed-off-by: Steffen Jaeckel <s@jaeckel.eu>