Python bindings to the Ed25519 public-key signature system.

This offers a comfortable python interface to a C implementation of the
Ed25519 public-key signature system (http://ed25519.cr.yp.to/), using the
portable 'ref' code from the 'SUPERCOP' benchmarking suite.

This system provides high (128-bit) security, short (32-byte) keys, short
(64-byte) signatures, and fast (2-6ms) operation. Please see the README for
more details.