add rb wrapper script

bin/bin/rb

@@ -0,0 +1,12 @@
+#!/usr/bin/env ruby
+
+def execute(_, code)
+  puts _.instance_eval(&code)
+rescue Errno::EPIPE
+  exit
+end
+
+single_line = ARGV.delete('-l')
+code = eval("Proc.new { #{ARGV.join(' ')} }")
+single_line ? STDIN.each { |l| execute(l.chomp, code) } : execute(STDIN.each_line, code)
+