This is an implementation of EdDSA in Java. Structurally, it
is based on the ref10 implementation in SUPERCOP (see
http://ed25519.cr.yp.to/software.html).

There are two internal implementations:

* A port of the radix-2^51 operations in ref10
- fast and constant-time, but only useful for Ed25519.
* A generic version using BigIntegers for calculation
- a bit slower and not constant-time, but compatible
with any EdDSA parameter specification.