Implement server mode.

This new mode works by first loading the model then listening for TCP
connections on a port. When a connection is received, arguments will be
parsed using a simple protocol:

- First the number of arguments will be read followed by a newline
  character.
- Then each argument will be read, separated by the 0 byte.
- With this we build an argument vector, similar to what is passed to
  the program entry point. We pass this to gpt_params_parse.

Finally `run` will be executed with the input/output streams connected
to the socket.

Signed-off-by: Thiago Padilha <thiago@padilha.cc>

utils.h

@@ -42,6 +42,10 @@ struct gpt_params {
     bool instruct          = false; // instruction mode (used for Alpaca models)
     bool ignore_eos        = false; // do not stop generating after eos
     bool perplexity        = false; // compute perplexity over the prompt
+
+#ifndef _WIN32
+    std::string listen_port = "";  // TCP port for when running in server mode
+#endif
 };
 
 bool gpt_params_parse(int argc, char ** argv, gpt_params & params);