improved some example descriptions

spec/time_travel/time_extensions.rb

@@ -0,0 +1,33 @@
+require 'time'
+
+module TimeTravel
+  module TimeExtensions
+  
+    def self.included(base)
+      base.extend(ClassMethods)
+      base.class_eval do
+        class << self
+          alias_method :immutable_now, :now
+          alias_method :now, :mutable_now
+        end
+      end
+      base.now = nil
+    end
+  
+    module ClassMethods
+
+      @@now = nil
+
+      def now=(time)
+        time = Time.parse(time) if time.instance_of?(String)
+        @@now = time
+      end
+
+      def mutable_now #:nodoc:
+        @@now || immutable_now
+      end
+    
+    end
+  
+  end
+end