Split backend and outgoing. Rename backend -> receive, client -> send.

receive.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <stdbool.h>
+
+#include "common.h"
+
+#define PARSER_STATE_LEN 256
+
+void receive_new(int, void *);
+void receive_print_usage();