Version 1.4.0

Version 1.4.0

* Added new functionality to encrypt/decrypt strings with Diffie-Hellman
key exchange with Nano addresses and private keys by converting the keys
to Curve25519 keys suitable for encryption and using Box functionality
from NaCl. The library will generate a random nonce to each encryption
and pass the nonce along with the encrypted message encoded in Base64
* Some code refactoring (use static classes and make sure ed25519 and
curve classes are always freshly created)