Fix bugs, add propper tests

std/io/mod.mcl

@@ -0,0 +1,12 @@
+
+fn write_str(fd: usize, s: &str) -> usize {
+    return __INTERNAL_syscall3(1, fd as &void, s->inner as &void, s->len as &void);
+}
+
+fn puts(s: &str) {
+    write_str(1, s);
+}
+
+fn eputs(s: &str) {
+    write_str(2, s);
+}