The ability to invoke other operation lists belongs in the new CallOp.
While we're here, make MacroOp.Add use a pointer receiver to match the
other methods.
Signed-off-by: Elias Naur <mail@eliasnaur.com>
Remembering the order of the corners in the RoundRect is difficult,
which suggest that RoundRect should be a struct with named fields.
Do that, and make Rect the special case where corner radii are all
zero.
Signed-off-by: Elias Naur <mail@eliasnaur.com>