Renamed Cxt and cleaned symmetric and asymmetric primitive classes

* Renamed Cxt to Key
* Removed spurious class members from Auth, Cipher, AuthEncrypt, Sign classes.
Fixed raaz packages with Cxt to Key renaming
Merge renaming Cxt to Key.
Removed R.C.Serialize. Fixes #189
bug in capital hex digit checking fixes #191.
Cleaned tests of raaz-cipher by using fromHex
Cleaned benchmarks of raaz-cipher by using fromHex
Removed some spurious inlines and extensions
Merge some test cleanup.