The IRC message class isn't fully implemented; make this clear

Also fixes the command definition for notify-host-by-irc

docs/messages.md

@@ -4,7 +4,7 @@ While [formatters](/docs/formatters.md) are crucial to contextualizing alerts, i
 
 ``nagios-herald`` provides a base Message class (``Message::Base``) from which all Message subclasses inherit.  ``Message::Base`` knows that all messages have content and recipients; it's the job of the Message subclasses to define additional behavior (such as how to send a message).
 
-Three message types are defined in ``nagios-herald``: Email, Pager, and IRC.  Feel free to cook up any new message types (i.e. CarrierPigeon, SmokeSignal) as you see fit.
+Three message types are defined in ``nagios-herald``: Email, Pager, and IRC.  The IRC class must be subclassed by a custom message class so that the ``send`` function can be implemented.  Feel free to cook up any new message types (i.e. CarrierPigeon, SmokeSignal) as you see fit.
 
 ## Getting Content into Messages
 

docs/nagios-config.md

@@ -34,8 +34,8 @@ define command {
 
 # IRC (optional)
 define command {
-    command_name    notify-service-by-irc
-    command_line    /usr/local/nagios-herald/bin/nagios-herald --message-type irc --formatter=$_SERVICEMESSAGE_FORMATTER_NAME$ --nagios-cgi-url=http://nagios.example.com/nagios/cgi-bin/cmd.cgi --reply-to=nagios@example.com
+    command_name    notify-host-by-irc
+    command_line    /usr/local/nagios-herald/bin/nagios-herald --message-type irc --formatter=$_HOSTMESSAGE_FORMATTER_NAME$ --nagios-cgi-url=http://nagios.example.com/nagios/cgi-bin/cmd.cgi --reply-to=nagios@example.com
 }
 
 define command {

lib/nagios-herald/messages/irc.rb

@@ -47,9 +47,7 @@ def send
           return
         end
 
-        # TODO: Actually make this send to an IRC server
-        # I expect the IRC server will be a value in the config
-        self.print
+        raise NotImplementedError.new("#{self.class.name}#send is an abstract method and must be implemented by a subclass.")
       end
 
     end