RT1665,2300: Crypto doc cleanups

RT1665: aes documentation.

Paul Green wrote a nice aes.pod file.
But we now encourage the EVP interface.
So I took his RT item and used it as impetus to add
the AES modes to EVP_EncryptInit.pod
I also noticed that rc4.pod has spurious references to some other
cipher pages, so I removed them.

RT2300: Clean up MD history (merged into RT1665)

Put HISTORY section only in EVP_DigestInit.pod. Also add words
to discourage use of older cipher-specific API, and remove SEE ALSO
links that point to them.

Make sure digest pages have a NOTE that says use EVP_DigestInit.

Review feedback:
More cleanup in EVP_EncryptInit.pod
Fixed SEE ALSO links in ripemd160.pod, sha.pod, mdc2.pod, blowfish.pod,
rc4.d, and des.pod.  Re-order sections in des.pod for consistency

Reviewed-by: Matt Caswell <matt@openssl.org>