directory for git submodules

* CLI11: cli argument parser
* cpr: curl for people, used by lokinet-bootstrap toolchain (to be removed)
* ghc-filesystem: `std::filesystem` shim lib for older platforms (like macos)
* ngtcp2: quic implementation
* nlohmann: json parser
* oxen-encoding: [bencode](https://www.bittorrent.org/beps/bep_0003.html#bencoding)/endian header-only library
* oxen-logging: spdlog wrapper library
* oxen-mq: zmq wrapper library for threadpool and rpc
* pybind11: for pybind modules
* sqlite_orm: for peer stats db
* uvw: libuv header only library for main event loop