change example code to do mrb_close()

I was hoping this would cause valgrind to complain less, but there is still
a lot of memory leaked (does mrb_close() actually free all of the managed
blocks?)  Anyway this helps somewhat and is good practice

src/codegen.c

@@ -2291,6 +2291,7 @@ p(fib(30), \"\\n\")\n\
   codedump_all(mrb, n);
 #endif
   mrb_run(mrb, mrb_proc_new(mrb, mrb->irep[0]), mrb_nil_value());
+  mrb_close(mrb);
 
   return 0;
 }

test/driver.c

@@ -55,6 +55,7 @@ main(void)
   else {
     /* no */
   }
+  mrb_close(mrb);
 
   return 0;
 }

tools/mirb/mirb.c

@@ -227,6 +227,7 @@ main(void)
       }
     }
   }
+  mrb_close(mrb_interpreter);
 
   return 0;
 }

tools/mrbc/mrbc.c

@@ -163,12 +163,14 @@ main(int argc, char **argv)
   if (n < 0 || args.rfp == NULL) {
     cleanup(&args);
     usage(argv[0]);
+    mrb_close(mrb);
     return n;
   }
 
   p = mrb_parse_file(mrb, args.rfp);
   if (!p || !p->tree || p->nerr) {
     cleanup(&args);
+    mrb_close(mrb);
     return -1;
   }
 
@@ -183,6 +185,7 @@ main(int argc, char **argv)
 
   if (n < 0 || args.check_syntax) {
     cleanup(&args);
+    mrb_close(mrb);
     return n;
   }
   if (args.initname) {
@@ -196,6 +199,7 @@ main(int argc, char **argv)
   }
 
   cleanup(&args);
+  mrb_close(mrb);
 
   return n;
 }

tools/mruby/mruby.c

@@ -130,6 +130,7 @@ cleanup(mrb_state *mrb, struct _args *args)
     mrb_free(mrb, args->cmdline);
   if (args->argv)
     mrb_free(mrb, args->argv);
+  mrb_close(mrb);
 }
 
 int