libarc - C++ Library with concepts and coroutine support

Benchmark:
clang++-11, Single-threaded
~270k requests/sec while Vertx is about ~142k

Running 10s test @ http://127.0.0.1:8086
  8 threads and 400 connections
  Thread Stats   Avg      Stdev     Max   +/- Stdev
    Latency     1.54ms    2.09ms 117.12ms   99.74%
    Req/Sec    34.27k     5.45k  116.16k    96.01%
  2735170 requests in 10.10s, 537.34MB read
Requests/sec: 270813.60
Transfer/sec:     53.20MB

Clang-format command:

$ find . -iname *.h -o -iname *.cc | xargs clang-format -i -style=file