Added hash key example.

examples/hash_key.rb

@@ -0,0 +1,33 @@
+require 'pp'
+require 'rubygems'
+require 'pathname'
+
+root_path = Pathname(__FILE__).dirname.join('..').expand_path
+lib_path  = root_path.join('lib')
+$:.unshift(lib_path)
+
+require 'toystore'
+
+class Track
+  include Toy::Store
+
+  adapter :memory, {}
+
+  key :hash, attributes: {
+    bucket: String,
+    track_id: SimpleUUID::UUID,
+  }
+end
+
+track = Track.new(:bucket => '2012')
+
+pp track.id
+# => {:bucket=>"2012", :track_id=> <UUID#70194110090200 time: 2012-11-19 16:40:24 -0500, usecs: 149874 jitter: 11675517131681036675>
+
+pp track.bucket # => "2012"
+pp track.track_id # => <UUID#70194110090200 time: 2012-11-19 16:40:24 -0500, usecs: 149874 jitter: 11675517131681036675>
+
+track.bucket = '2011'
+
+pp track.id # => :bucket is now "2011"
+pp track.id_changed? # => true