When configured for more than one collection, v0.3.2 produces empty TOCs of children in all but the last collection, due to referencing the overwritten `pages_list` in `_layouts/default.html`. When the same parent title is used in different collections, v0.3.2 can also produce a link to the wrong collection. Moreover, v0.3.3  can also produce incorrect breadcrumb links; see issue just-the-docs#492.

- Move the breadcrumbs link variable assignments from `_layouts/default.html` to `_includes/nav.html`, and make it conditional on `page` being in the current collection.

- Correct the condition for assignment to `second_level_url`, as in just-the-docs#477.

- Change the variable used for the TOC from `children_list` to `toc_list`, move its assignment from `_layouts/default.html` to `_includes/nav.html`, and make it conditional on `page` being in the current collection.

- Add regression tests for TOC/breadcrumb links in multiple collections, with configuration commented-out.

With the v0.3.3 regression tests active, `diff -r -q` on `_site/docs` reports that only `_site/docs/tests/navigation/disambiguation/dca/index.html` differs, which is due to the breadcrumb correction there.

- Fix a bug with the breadcrumbs list, where a link on a grandchild page can point to the wrong parent page, following the solution suggested by @AdityaTiwari2102 in just-the-docs#477

Manually merge the relevant changes from PR just-the-docs#494, namely:

When configured for more than one collection, v0.3.2 produces empty TOCs of children in all but the last collection, due to referencing the overwritten `pages_list` in `_layouts/default.html`. When the same parent title is used in different collections, v0.3.2 can also produce a link to the wrong collection. Moreover, v0.3.3  can also produce incorrect breadcrumb links; see issue just-the-docs#492.

- Move the breadcrumbs link variable assignments from `_layouts/default.html` to `_includes/nav.html`, and make it conditional on `page` being in the current collection.

- Correct the condition for assignment to `second_level_url`, as in just-the-docs#477.

- Change the variable used for the TOC from `children_list` to `toc_list`, move its assignment from `_layouts/default.html` to `_includes/nav.html`, and make it conditional on `page` being in the current collection.

Extension of PR just-the-docs#977 to v0.4.0.rc1:

- Make callouts `loud`.
- Replace a warning paragraph by a callout.
- Use a reference link instead of an explicit url for @pmarsceill .
- Add link reference definitions for PRs and new contributors in v0.4.0.rc1.
- Replace inline urls by shortcut link references.

The changes to replace URLs by link references would be too tedious and error-prone to do completely manually for v0.4.0.rc1.
The following regexp replacements were applied to the sections of v0.4.0.rc1, using Atom:

- Copy a section of changes.
- In the copy, replace `.*(https://.*pull/)([0-9]+).*$` by `[#$2]: $1$2`.
- In the original, replace `(https://.*pull/)([0-9]+)` by `[#$2]`.

- Copy a section of new contributors.
- In the copy, replace `\* @([^ ]+) .*$` by `[@$1]: https://githhub.com/$1`.
- In the original, replace `@([a-zA-Z0-9]+)` by `[@$1]`.

Add (co)authors in [just-the-docs#578]:

* [@AdityaTiwari2102] made their first contribution in [just-the-docs#477]
* [@svrooij] made their first contribution in [just-the-docs#544]

[@AdityaTiwari2102]: https://githhub.com/AdityaTiwari2102
[@svrooij]: https://githhub.com/svrooij

To test:

1. Check that the CHANGELOG contents looks the same in the docs and in the repo (apart from the callouts) with clickable links to all PRs and contributors for v0.4.0.rc1.

2. Check that none of the lines with changes or new contributors have been removed.

* Make more CHANGELOG  urls clickable

Extension of PR #977 to v0.4.0.rc1:

- Make callouts `loud`.
- Replace a warning paragraph by a callout.
- Use a reference link instead of an explicit url for @pmarsceill .
- Add link reference definitions for PRs and new contributors in v0.4.0.rc1.
- Replace inline urls by shortcut link references.

The changes to replace URLs by link references would be too tedious and error-prone to do completely manually for v0.4.0.rc1.
The following regexp replacements were applied to the sections of v0.4.0.rc1, using Atom:

- Copy a section of changes.
- In the copy, replace `.*(https://.*pull/)([0-9]+).*$` by `[#$2]: $1$2`.
- In the original, replace `(https://.*pull/)([0-9]+)` by `[#$2]`.

- Copy a section of new contributors.
- In the copy, replace `\* @([^ ]+) .*$` by `[@$1]: https://githhub.com/$1`.
- In the original, replace `@([a-zA-Z0-9]+)` by `[@$1]`.

Add (co)authors in [#578]:

* [@AdityaTiwari2102] made their first contribution in [#477]
* [@svrooij] made their first contribution in [#544]

[@AdityaTiwari2102]: https://githhub.com/AdityaTiwari2102
[@svrooij]: https://githhub.com/svrooij

To test:

1. Check that the CHANGELOG contents looks the same in the docs and in the repo (apart from the callouts) with clickable links to all PRs and contributors for v0.4.0.rc1.

2. Check that none of the lines with changes or new contributors have been removed.

* Revert to quiet callouts