Add external links for posts

[choldgraf]

Description

This PR adds support for external links for posts, by adding an external_link parameter to the Post directive and page-level metadata. If this parameter is given, then when post lists or collections are created, the link will point to external_link rather than using an internal ref to the page.

This is a common pattern in a few other static site generators, since people may want to link to posts in some external site occasionally (such as Medium, or another blog).

To Do

• [x] Confirm that the implementation looks OK
• [x] Confirm the docs look correct
• [ ] Write tests as needed

Fixes #110

[nabobalis]

The implementation looks good to me.

[SilverRainZ]

Any progress?

[choldgraf]

Hey all - it has been a while since I looked at this one, but if folks would find it useful I can try to make time to get it done. What do others think?

[nabobalis]

Hi @choldgraf, if you would prefer, I could take over and try to get this over the finish line?

[choldgraf]

I'm more than happy for that to happen - you will probably be a lot more effective at that than I am, since you have more context on the ablog infrastructure 🙏

Let know if I can be helpful in some way!

[nabobalis]

Works nicely if you see https://ablog--112.org.readthedocs.build/blog/category/manual/

Now to decide on tests.

[nabobalis]

TODO: Work out why locations is not at the sidebar for the doc build.

[nabobalis]

Sorry I forgot about this.

I've added a test, I will backport this to the 0.10 branch and do a release today.