Added some tests for stdio

tests/stdio/fwrite.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+
+int main(int argc, char ** argv) {
+	FILE *f = fopen("stdio/fwrite.out", "w");
+	char *in = "Hello World!";
+	fputs(in, f); // calls fwrite, helpers::fwritex, internal::to_write and internal::stdio_write
+	fclose(f);
+	return 0;
+}