Fix compatibility with newer digest gems (#29)

Fix: #27
Ref: ruby/digest#58
Ref: ruby/digest#59

.gitignore

@@ -10,6 +10,8 @@
 *.gem
 *.log
 *.rbc
+*.bundle
+*.bundle.dSYM
 /.config
 /.rake_tasks~
 /coverage/

ext/digest/extconf.rb

@@ -27,5 +27,6 @@ def have_func!(header, *args)
 have_header! "string.h"
 
 have_func! "rb_str_set_len"
+have_func "rb_digest_make_metadata", "ruby/digest.h"
 
 create_makefile "digest/keccak" or exit 1

ext/digest/keccak.c

@@ -144,7 +144,11 @@ Init_keccak() {
 
 	cKeccak = rb_define_class_under(mDigest, "Keccak", cDigest_Base);
 
+#ifdef HAVE_RB_DIGEST_MAKE_METADATA
+	rb_iv_set(cKeccak, "metadata", rb_digest_make_metadata(&keccak));
+#else
 	rb_iv_set(cKeccak, "metadata", Data_Wrap_Struct(0, 0, 0, (void *)&keccak));
+#endif
 
   rb_define_method(cKeccak, "initialize", rb_keccak_initialize, -1);
   rb_define_method(cKeccak, "digest_length", rb_keccak_digest_length, 0);