[PyX-user] page_ kwargs of canvas.writexxx

[Alan G. Isaac]

More user feedback.
Please consider adding this to the first paragraph of the `Class canvas` documentation.

Note that the writeXXX methods of a canvas construct a single page document,
passing kwargs to the document.page constructor and to the `writeXXX`
method of a document.document instance.
(To pass a `page` kwarg, preface it with `page_`;
to pass a `write` kwarg`, preface it with `write_`.

Also, please consider augmenting the interface.
It would be better from this user's perspective
to provide keywords `page` and `write` that would
each accept a dict of appropriate keywords (without
the prefixes).

Thanks!
Alan Isaac