Add rijndael-cbc@lysator.liu.se.

Add the rijndael-cbc@lysator.liu.se cipher as an alias for aes256-cbc.
Provide a better link to OpenSSH's extensions.
Move OpenSSH extensions to separate directories.
Fix several namespace issues.
Added support for RFC 4252.

Adds support for the 4 authentication methods defined in RFC 4252:
* "none" (used only to list available authentication methods)
* "password"
* "publickey"
* "hostbased"