Add hash algorithms SHA-512/224 and SHA-512/256

The hash algorithms SHA-512/224 and SHA-512/256 are two of the seven
FIPS 180-4, Secure Hash Standard Approved algorithms for generating a
condensed representation of a message (message digest).

http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf

Test values of the implementation of SHA-512/224 and SHA-512/256 are
available here:

http://csrc.nist.gov/groups/ST/toolkit/documents/Examples/SHA512_224.pdf
http://csrc.nist.gov/groups/ST/toolkit/documents/Examples/SHA512_256.pdf
http://csrc.nist.gov/groups/ST/toolkit/documents/Examples/SHA2_Additional.pdf

With id-sha512-224 and id-sha512-256 NIST has registered two Secure Hash
Algorithm object identifiers:

http://csrc.nist.gov/groups/ST/crypto_apps_infra/csor/algorithms.html#Hash

With sha512-224WithRSAEncryption and sha512-256WithRSAEncryption two
OIDs for RSA signatures are defined in the PKCS #1 Version 2.2 RSA
Cryptography Standard:

http://www.emc.com/emc-plus/rsa-labs/pkcs/files/h11300-wp-pkcs-1v2-2-rsa-cryptography-standard.pdf
ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-2.asn