Creates a new window class object. Allowed %OPTIONS are:
-name => STRING
the name for the class (it must be unique!).
-icon => Win32::GUI::Icon object
-cursor => Win32::GUI::Cursor object
-color => COLOR or Win32::GUI::Brush object
the window background color.
-menu => STRING
a menu name (not yet implemented).
-extends => STRING
name of the class to extend (aka subclassing).
-widget => STRING
name of a widget class to subclass; currently available are:
Button, Listbox, TabStrip, RichEdit.
-style => FLAGS
use with caution!