[PYTHON-CRYPTO] aes library

[Paul Rubin]

1. I think CLE mode should be folded into CTR mode.  Just pass an
optional arg to the CTR mode constructor specifying the endianness you
want.

2. I'd like to see more justification for supporting all those modes
than "they're in the standard".

3. If CFB mode is supported, arbitary CFB feedback sizes should be
supported (as long as the feedback size divides the block size).

4. Making the Python app handle padding is a big slowdown when the
messages are short.  The C library should handle padding per PKCS #5.
If there's a standard for ciphertext stealing and other applications
use it, then support that too.  Otherwise skip it.