Based on UNIX sockets to avoid the vagaries of FIFOs
in asynchronous mode. Currently unlinks stale sockets
before binding and cleans them up again after shutdown.
Instead of uv_shutdown, uv_write, uv_connect taking raw uv_req_t we subclass
uv_req_t into uv_shutdown_t, uv_write_t, and uv_connect_t.
uv_req_init is removed.