Added an example

New examples folder.  Only has one at the moment: 
an async message send.

examples/async_message.rb

@@ -0,0 +1,28 @@
+require 'rubygems'
+require 'pusher'
+require 'eventmachine'
+require 'em-http-request'
+
+# To get these values:
+# - Go to https://app.pusherapp.com/
+# - Click on Choose App.
+# - Click on one of your apps
+# - Click API Access
+Pusher.app_id = 'your_app_id'
+Pusher.key = 'your_key'
+Pusher.secret = 'your_secret'
+
+
+EM.run {
+  deferrable = Pusher['test_channel'].trigger_async('my_event', 'hi')
+
+  deferrable.callback { # called on success
+    puts "Message sent successfully."
+    EM.stop
+  }
+  deferrable.errback { |error| # called on error
+    puts "Message could not be sent."
+    puts error
+    EM.stop
+  }
+}