redirects

Describe the bug

If I have one page, a.md that has some relative links in it:

[X](./some/path/to/x.md)

And I use include_relative to include the content of b.md in another page:

{% include_relative a.md %}

In the generated a.html, the links will correctly point to x.html. But on b.html, the links will point to b.md.

Right now even contributors can see and create redirects. This might not be ideal so we should at least restrict it to those with publishing caps or even just to admins.

If we make it easy to change who has access via a filter or just documenting using the roles API then I think restricting to admins is the right call.