We're about to reduce the scope of the Window.Queue by moving it
to FrameEvent. As a consequence, Context can no longer rely on a
Queue constant over its lifetime.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
While here, unexport the Queue and Config fields. The NewContext
cosntructor is shorter, and there is no reason to expose the fields
to accidental mutation.
Signed-off-by: Elias Naur <mail@eliasnaur.com>