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>

tcp_server.h

@@ -0,0 +1,7 @@
+#pragma once
+
+#include "utils.h"
+#include "llama.h"
+#include "run.h"
+
+int listen_tcp(llama_context * ctx, gpt_params params);