make mrb_hash_keys() non static function

include/mruby/hash.h

@@ -28,6 +28,7 @@ mrb_value mrb_hash_get(mrb_state *mrb, mrb_value hash, mrb_value key);
 mrb_value mrb_hash_fetch(mrb_state *mrb, mrb_value hash, mrb_value key, mrb_value def);
 mrb_value mrb_hash_delete_key(mrb_state *mrb, mrb_value hash, mrb_value key);
 mrb_value mrb_hash(mrb_state *mrb, mrb_value obj);
+mrb_value mrb_hash_keys(mrb_state *mrb, mrb_value hash);
 
 /* RHASH_TBL allocates st_table if not available. */
 #define RHASH(obj)   ((struct RHash*)((obj).value.p))

src/hash.c

@@ -965,7 +965,7 @@ mrb_hash_to_hash(mrb_state *mrb, mrb_value hash)
  *
  */
 
-static mrb_value
+mrb_value
 mrb_hash_keys(mrb_state *mrb, mrb_value hash)
 {
   khash_t(ht) *h = RHASH_TBL(hash);