Page.context_object_name can be used to define a more meaningful name
for the page variable in the template.
If defined, the default `page` and `self` are still available for use in
shared templates.
Resolves #5213
Most of the samples were already 4-space indented, but a few were using 2-space,
which is both inconsistent and, when it happened with Python code samples,
incompatible with PEP8.
Generating links with `link text <./path/to/doc#anchor>`__ does not work for html.
It produces a link to `./path/to/doc#anchor` instead of `./path/to/doc.html#anchor`.
It would be tempting to add `.html` before `#` but would likely cause some more issues
when generating the documentation as pdf or epub.
References on the other hand will work regardless of the output format.
All `.. code::` instances have been changed to use `.. code-block::`,
and have been properly formatted. The syntax names have been normalised,
so all django templates use the `html+django` syntax, shell commands use
`sh`, and plain text uses `text`.
