Fixed documentaion in CryptoMode
renamed digestCxt to toDigest
Merge added cryptographic modes of operation

- Support for Encrypt, Decrypt, Verify, Auth, and AuthEnc and
  VerifyDecrypt operations.
moved the raaz-primitives directory to raaz-core
updated cabal file
updated the package list in Makefile
update Makefile
update dependency in raaz-hash
reduced the lower bound on integer-gmp and commented the benchmark
added the Raaz/Number.hs module
removed raaz-modular from the modules that are installed
Merge renaming of raaz-primitive to raaz-core partially fixes #126

This is just a renaming. We would like to clean up the package
hierarchy.
Fixed unassigned buffer bug in raaz-random
Added way to parse BE Words
RSA PKCS Signature scheme added
Added Diffie Hellman Key exchange