Add BIP32-Ed25519 implementation

[semuxgo]

Resolves issue #171

There is no standards for the extended keys format, so we propose the follow specs:

	..	chain code	key data
Extended Private Key	..	c (32 bytes)	kL (32 bytes) + kR (32 bytes)
Extended Public Key	..	c (32 bytes)	A (32 bytes)