Fixed lots of subtle bugs, sped up Hint()

Many thanks to GNUnet's commented version of the original Ed25519.java class:
https://gnunet.org/svn/gnunet-java/src/main/java/org/gnunet/util/crypto/
Moved Hint() to Utils
Use bitflips instead of calc for a

Saves ~0.4ms per key when running signing tests.
Todo: are these bitflips the same for any hash function?