Added symmetric authentication to simlify hmac
Added functions to generate and verify authentication tags for the given gadget
Changed Auth to Sign in RSA
Fixed raaz-cipher according to changed definition of Key type family
Fixed raaz-random according to changed definition of Key
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.