Add ed25519 precompiled contract

[tell-1c]

🚀 Feature Request

Add support for ed25519 signature verification in smart contracts.

Motivation

The proposal suggests adding support for the ed25519 elliptic curve as used in Semux.

This issue was discussed in the Ethereum community and there is a corresponding EIP
https://github.com/ethereum/EIPs/blob/master/EIPS/eip-665.md