Modify `Range#initialize` to accept optional `exclusive` argument.

src/range.c

@@ -125,11 +125,15 @@ mrb_value
 mrb_range_initialize(mrb_state *mrb, mrb_value range)
 {
   mrb_value beg, end;
-  mrb_value flags;
+  int exclusive;
+  int n;
 
-  mrb_get_args(mrb, "ooo", &beg, &end, &flags);
+  n = mrb_get_args(mrb, "oo|b", &beg, &end, &exclusive);
+  if (n != 3) {
+    exclusive = 0;
+  }
   /* Ranges are immutable, so that they should be initialized only once. */
-  range_init(mrb, range, beg, end, mrb_test(flags));
+  range_init(mrb, range, beg, end, exclusive);
   return range;
 }
 /*
@@ -444,7 +448,7 @@ mrb_init_range(mrb_state *mrb)
   mrb_define_method(mrb, r, "exclude_end?",    mrb_range_excl,        ARGS_NONE());      /* 15.2.14.4.6  */
   mrb_define_method(mrb, r, "first",           mrb_range_beg,         ARGS_NONE());      /* 15.2.14.4.7  */
   mrb_define_method(mrb, r, "include?",        mrb_range_include,     ARGS_REQ(1));      /* 15.2.14.4.8  */
-  mrb_define_method(mrb, r, "initialize",      mrb_range_initialize,  ARGS_REQ(4));      /* 15.2.14.4.9  */
+  mrb_define_method(mrb, r, "initialize",      mrb_range_initialize,  ARGS_ANY());       /* 15.2.14.4.9  */
   mrb_define_method(mrb, r, "last",            mrb_range_end,         ARGS_NONE());      /* 15.2.14.4.10 */
   mrb_define_method(mrb, r, "member?",         mrb_range_include,     ARGS_REQ(1));      /* 15.2.14.4.11 */