Implement printf (very simple version)

tests/printf.c

@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main(int argc, char ** argv) {
+    printf(
+        "percent: %%\nstring: %s\nchar: %c\nint: %d\nuint: %u\nhex: %x\nHEX: %X\nstring: %s\n",
+        "String",
+        'c',
+        -16,
+        32,
+        0xbeef,
+        0xC0FFEE,
+        "end"
+    );
+    return 0;
+}