getting rid of fillUp and fillUpChunks

Use the stuff coming from Raaz.ByteSource instead.
renamed startCxt to startHashCxt
exposed a rudimentry MAC module
added rfc2104 for mac construction
added the HMAC datatype and instances for BlockPrimitives and HasPadding
added MAC instance for HMAC
Merge branch 'x-primitives'

Merging MAC module with HMAC construction
renamed startCxt to startHashCxt every where

This is due to change in the name in the raaz-primitives package.
Merge branch 'x-hash-sha'