io1: Add printf examples

Signed-off-by: Louis Solofrizzo <lsolofrizzo@online.net>

unikernel-demo/io1/printf/Makefile

@@ -0,0 +1,3 @@
+export ukl-obj-m := main.o
+
+include ../../Makefile

unikernel-demo/io1/printf/main.c

@@ -0,0 +1,25 @@
+#include <stdio.h>
+
+#ifndef USERSPACE
+#define main ukl_main
+#endif
+
+typedef struct {
+    char a;
+    char *b;
+    int c;
+} test_t;
+
+int main(void) {
+    char        str[250];
+    test_t      test = {
+        .a = 'a',
+        .b = "Hello!",
+        .c = 10
+    };
+
+    printf("a = %c, b = %s, c = %d\n", test.a, test.b, test.c);
+    snprintf(str, sizeof(str), "a = %c, b = %s, c = %d\n", test.a, test.b, test.c);
+    puts(str);
+    return 0;
+}