The "Page models" documentation page in the Wagtail usage guide has
several broken links (see current page at
https://docs.wagtail.io/en/stable/topics/pages.html).
These links work when developing the documentation locally, but not when
served on ReadTheDocs (docs.wagtail.io)
The broken links are all of the form /some/page.html#anchor - somehow
this format doesn't translate properly to get the necessary RTD prefix
(for example /en/stable/).
I've modified these links to use RST references, which will also make
them more robust to future changes.
Documentation examples of `Page.get_context` and `Page.get_template`
lack `*args` and `**kwargs` parameters (which were added way back in
8c4c268641).
This commit adds those missing parameters.
