clean: split code in multiple files

src/print.c

@@ -0,0 +1,15 @@
+
+
+#include <stdarg.h>
+#include <stdio.h>
+
+void print_err(const char *format, ...)
+{
+    va_list args;
+
+    puts("ft_ping: ");
+    va_start(args, format);
+    vprintf(format, args);
+    va_end(args);
+    putchar('\n');
+}