Update TODO file.
Move PublicKey\SSH\ED25519\Params to ED25519.

Rename \fpoirotte\Pssht\PublicKey\SSH\ED25519\Params
into just \fpoirotte\Pssht\ED25519.

This is just a slight cleanup to avoid logs about this class not defining
any valid public key algorithm.
Update README and prepare Curve25519 support.