Added fromByteString and fromByteStringStorable in Raaz.Util.ByteString
Optimized Reference Implementation of AES

* Now uses 32Bit words instead of 4 x 8Bit Words similar to CPortable version.
* Speed now only 3 times slower than cportable version as compared to previously being around 90 times slower.
Made AES IV more typesafe by using specific types instead of ByteString
Merge some improvements to AES

1. AES IV now not a plain bytestring.

2. Some optimisations to refrence implementation.