* Change private representation of events
  
Using a struct is too brittle (you have to worry about
vtable-offset-user, have to create new struct types, etc). We should use
a standard type. An alist would be nice, but vectors might be noticeably
more efficient. Dunno.

* Add a toplevel GDK module

GDK isn't finished, of course, and it won't be until someone writes an
app that uses it.

