added .gitignore
document the Hash class
added the HMAC primitive
removed some unwanted imports from R.P.Hash
added length safe version of replicate function
some code and documentation cleanup
added memory buffer to hash cryptographic hashes
added gadget instance for HMAC
HMAC gadget instances implemented.
Merge some design change to simplify primitives

- We now have the notion of symmetric and asymmetric primitives
Merge hmac implementation
SHA1: Template haskell removed, fixes #72
SHA256: Template haskell removed, fixes #72
SHA512: Template haskell removed, fixes #72
raaz-hash.cabal: Template haskell removed, fixes #72
Raaz.Types: Template haskell removed, fixes #72
Raaz.Util.TH: Template haskell removed, fixes #72
Raaz.Hash.Sha224.Type: fixed warning due to import
Merge got rid of template haskell based implementation fixes #72.
Added hmac and hmac'