Add Support for TurtleCoin Upcoming Fork

[brandonlehmann]

TurtleCoin Release Notes: https://github.com/turtlecoin/turtlecoin/releases/latest
Added as algorithm: cryptonight_turtle

Note: Auto-switching is not possible with this PR as TurtleCoin uses a parent/root block header that results in the pools (and thus the miners) always seeing the block MajorVersion as 1 (unless it's updated as part of a fork). We don't currently do this and have no immediate plans to do so; however, please see PR #2177 which adds support for using a MajorBlock version supplied by a pool with support to do so.

Addresses #2159 & #2174

Dero Gold is already using the algorithm, you can test the build against one of their pools

"pool_list": [
  {
    "pool_address": "dego.cnpool.cc:32550",
    "wallet_address": "dg5GFxdp1x8Ehux7wJez9wiuMGearHW9m3YpCQDjBdk5ZgWVK12uD36VWGgm1J6TqCYh4Wr8FGutCKDWC1xfjefR1AKSW7ZxE",
    "rig_id": "x",
    "pool_password": "x",
    "use_nicehash": false,
    "use_tls": false,
    "tls_fingerprint": "",
    "pool_weight": 1
  }
],
"currency": "cryptonight_turtle"