Add default delay range, configure check

lib/twitter_ebooks/bot.rb

@@ -180,12 +180,17 @@ module Ebooks
       @seen_tweets ||= {}
 
       @username = username
+      @delay_range ||= 1..6
       configure
 
       b.call(self) unless b.nil?
       Bot.all << self
     end
 
+    def configure
+      raise ConfigurationError, "Please override the 'configure' method for subclasses of Ebooks::Bot."
+    end
+
     # Find or create the conversation context for this tweet
     # @param tweet [Twitter::Tweet]
     # @return [Ebooks::Conversation]