Refactor for libtorrent 2.0

[tjjh89017]

Development environment: Debian sid

Must

• [x] singleton for easy grpc
• [ ] log for debug (need torrent status) SPDLOG sudo apt install libspdlog-dev
• [ ] re-write disk_interface (only disk_interface could create disk_buffer_holder and pass it to job)
  • [ ] re-write mmap_storage (4th)
  • [ ] write buffer_pool (3rd)
    • [ ] read pool
    • [ ] write pool
  • [ ] threading pool (std::thread, not pthread) (1st)
  • [ ] job pool (2nd)
  • [ ] update README.md (5th)

Optional

• [ ] dial out mode for controller
  • [ ] controller could get seq to setup 1 to 1 peer