Switch Threefish256 over to a wrapped C implementation.
Clean up some warnings.
Replace take + drop with splitAt in hash256.
Pass the tweak to c_en/decrypt256 as two words instead of an array.
Add -O2 to the C sources for good measure.
Use Data.ByteString.replicate rather than Data.ByteString.pack + replicate.
More strictness annotations!
Update README.