Add more POD to Pluggable.

Add more POD to FlatRate.pm, for the to be written calculate method.
Build create and new methods for Ship, convert existing code to throw exceptions.
Tests for Ship, that look suspiciously similar to ShipDriver.

lib/WebGUI/Pluggable.pm

@@ -46,7 +46,7 @@ These functions are available from this package:
 
 #-------------------------------------------------------------------
 
-=head2 instanciate ( module, method, params )
+=head2 instanciate ( module, sub, params )
 
 Dynamically ensures that a plugin module is loaded into memory. Then instanciates a new object from the module. Croaks on failure.
 
@@ -54,6 +54,15 @@ Dynamically ensures that a plugin module is loaded into memory. Then instanciate
 
 The name of the module you'd like to load like "WebGUI::Asset::Snippet";
 
+=head3 sub
+
+The name of the constructor you would like to invoke from the module.  Usually "new", or sometimes "create".
+
+=head3 params
+
+An array ref of params to send to the constructor.  In WebGUI, the first param should be a WebGUI::Session
+object.
+
 =cut
 
 sub instanciate {