Added gemspec for readline gem that is wrapper library for reline and readline extension

doc/maintainers.rdoc

@@ -232,6 +232,10 @@ Zachary Scott (zzak)
   Aaron Patterson (tenderlove), Hiroshi SHIBATA (hsbt)
   https://github.com/ruby/racc
   https://rubygems.org/gems/racc
+[lib/readline.rb]
+  aycabta
+  https://github.com/ruby/readline
+  https://rubygems.org/gems/readline
 [lib/rdoc.rb, lib/rdoc/*]
   Eric Hodel (drbrain), Hiroshi SHIBATA (hsbt)
   https://github.com/ruby/rdoc

lib/readline.gemspec

@@ -0,0 +1,23 @@
+Gem::Specification.new do |spec|
+  spec.name          = 'readline'
+  spec.version       = '0.0.1.pre.1'
+  spec.authors       = ['aycabta']
+  spec.email         = ['aycabta@gmail.com']
+
+  spec.summary       = %q{It's a loader for "readline".}
+  spec.description   = <<~EOD
+    This is just loader for "readline". If Ruby has "readline-ext" gem that
+    is a native extension, this gem will load its first. If Ruby doesn't have
+    the "readline-ext" gem this gem will load "reline" that is a compatible
+    library with "readline-ext" gem and is implemented by pure Ruby.
+  EOD
+  spec.homepage      = 'https://github.com/ruby/readline'
+  spec.license       = 'Ruby license'
+
+  spec.files         = Dir['BSDL', 'COPYING', 'README.md', 'lib/readline.rb']
+  spec.require_paths = ['lib']
+
+  spec.add_runtime_dependency 'reline'
+  spec.add_development_dependency 'bundler'
+  spec.add_development_dependency 'rake'
+end

tool/sync_default_gems.rb

@@ -42,6 +42,7 @@
 # * https://github.com/ruby/net-pop
 # * https://github.com/ruby/net-smtp
 # * https://github.com/ruby/cgi
+# * https://github.com/ruby/readline
 #
 
 require 'fileutils'
@@ -91,6 +92,7 @@ $repositories = {
   netpop: "ruby/net-pop",
   netsmtp: "ruby/net-smtp",
   cgi: "ruby/cgi",
+  readline: "ruby/readline",
 }
 
 def sync_default_gems(gem)