Move digest.rb back under ext as the extension bundled library

Author: nobu

digest.gemspec

@@ -14,16 +14,31 @@ Gem::Specification.new do |spec|
 
   spec.files         = [
     "LICENSE.txt", "README.md",
-    "ext/digest/bubblebabble/bubblebabble.c", "ext/digest/bubblebabble/extconf.rb", "ext/digest/defs.h",
-    "ext/digest/digest.c", "ext/digest/digest.h", "ext/digest/digest_conf.rb", "ext/digest/extconf.rb",
-    "ext/digest/md5/extconf.rb", "ext/digest/md5/md5.c", "ext/digest/md5/md5.h", "ext/digest/md5/md5cc.h",
-    "ext/digest/md5/md5init.c", "ext/digest/rmd160/extconf.rb", "ext/digest/rmd160/rmd160.c",
-    "ext/digest/rmd160/rmd160.h", "ext/digest/rmd160/rmd160init.c", "ext/digest/sha1/extconf.rb",
-    "ext/digest/sha1/sha1.c", "ext/digest/sha1/sha1.h", "ext/digest/sha1/sha1cc.h",
-    "ext/digest/sha1/sha1init.c", "ext/digest/sha2/extconf.rb", "ext/digest/sha2/lib/sha2.rb",
-    "ext/digest/sha2/sha2.c", "ext/digest/sha2/sha2.h", "ext/digest/sha2/sha2cc.h",
-    "ext/digest/sha2/sha2init.c", "ext/digest/test.sh", "ext/openssl/deprecation.rb",
-    "lib/digest.rb"
+
+    "ext/digest/defs.h", "ext/digest/digest.c", "ext/digest/digest.h",
+    "ext/digest/digest_conf.rb", "ext/digest/extconf.rb",
+    "ext/digest/lib/digest.rb",
+
+    "ext/digest/bubblebabble/bubblebabble.c",
+    "ext/digest/bubblebabble/extconf.rb",
+
+    "ext/digest/md5/extconf.rb", "ext/digest/md5/md5.c",
+    "ext/digest/md5/md5.h", "ext/digest/md5/md5cc.h",
+    "ext/digest/md5/md5init.c",
+
+    "ext/digest/rmd160/extconf.rb", "ext/digest/rmd160/rmd160.c",
+    "ext/digest/rmd160/rmd160.h", "ext/digest/rmd160/rmd160init.c",
+
+    "ext/digest/sha1/extconf.rb", "ext/digest/sha1/sha1.c",
+    "ext/digest/sha1/sha1.h", "ext/digest/sha1/sha1cc.h",
+    "ext/digest/sha1/sha1init.c",
+
+    "ext/digest/sha2/extconf.rb", "ext/digest/sha2/lib/sha2.rb",
+    "ext/digest/sha2/sha2.c", "ext/digest/sha2/sha2.h",
+    "ext/digest/sha2/sha2cc.h", "ext/digest/sha2/sha2init.c",
+
+    "ext/openssl/deprecation.rb",
+    "ext/digest/test.sh",
   ]
 
   spec.required_ruby_version = ">= 2.5.0"