Promote singleton to default gems

lib/singleton/singleton.gemspec

@@ -0,0 +1,27 @@
+begin
+  require_relative "lib/singleton/version"
+rescue LoadError # Fallback to load version file in ruby core repository
+  require_relative "version"
+end
+
+Gem::Specification.new do |spec|
+  spec.name          = "singleton"
+  spec.version       = Singleton::VERSION
+  spec.authors       = ["Yukihiro Matsumoto"]
+  spec.email         = ["matz@ruby-lang.org"]
+
+  spec.summary       = %q{The Singleton module implements the Singleton pattern.}
+  spec.description   = spec.summary
+  spec.homepage      = "https://github.com/ruby/singleton"
+  spec.license       = "BSD-2-Clause"
+
+  spec.metadata["homepage_uri"] = spec.homepage
+  spec.metadata["source_code_uri"] = spec.homepage
+
+  spec.files         = Dir.chdir(File.expand_path('..', __FILE__)) do
+    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
+  end
+  spec.bindir        = "exe"
+  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.require_paths = ["lib"]
+end

lib/singleton/version.rb

@@ -0,0 +1,3 @@
+module Singleton
+  VERSION = "0.1.0"
+end