add ruby websocket bencharking code using

faye-websocket-ruby to receive messages as fast as possible

test/compatibility/ruby/README.md

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+```
+export GEM_HOME=$HOME/local/gems
+bundle install faye-websocket
+```
+
+https://stackoverflow.com/questions/486995/ruby-equivalent-of-virtualenv

test/compatibility/ruby/devnull_client.rb

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+#
+# $ ruby --version
+# ruby 2.6.3p62 (2019-04-16 revision 67580) [universal.x86_64-darwin19]
+# 
+# Install a gem locally by setting GEM_HOME
+# https://stackoverflow.com/questions/486995/ruby-equivalent-of-virtualenv
+# export GEM_HOME=$HOME/local/gems
+# bundle install faye-websocket
+#
+# In a different terminal, start a push server:
+# $ ws push_server -q
+#
+# $ ruby devnull_client.rb
+# [:open]
+# Connected to server
+# messages received per second: 115926
+# messages received per second: 119156
+# messages received per second: 119156
+# messages received per second: 119157
+# messages received per second: 119156
+# messages received per second: 119156
+# messages received per second: 119157
+# messages received per second: 119156
+# messages received per second: 119156
+# messages received per second: 119157
+# messages received per second: 119156
+# messages received per second: 119157
+# messages received per second: 119156
+# ^C[:close, 1006, ""]
+# 
+require 'faye/websocket'
+require 'eventmachine'
+
+EM.run {
+  ws = Faye::WebSocket::Client.new('ws://127.0.0.1:8008')
+
+  counter = 0
+
+  EM.add_periodic_timer(1) do
+    print "messages received per second: #{counter}\n"
+    counter = 0  # reset counter
+  end
+
+  ws.on :open do |event|
+    p [:open]
+    print "Connected to server\n"
+  end
+
+  ws.on :message do |event|
+    # Uncomment the next line to validate that we receive something correct
+    # p [:message, event.data]
+    counter += 1
+  end
+
+  ws.on :close do |event|
+    p [:close, event.code, event.reason]
+    ws = nil
+  end
+}