[Security] Bump mixin-deep from 1.3.1 to 1.3.2

Bump @primer/css from 12.6.0 to 12.7.0

Allow for custom overrides by the user

Fix trailing comma bug in search-data.json

Improvement/site logo

Update nav.html to eliminate generation of undisplayed elements

Improve heading anchors

Recommend using index.md as parent page for sections

Introduces the possibility for a summary in the table of contents

Bumps [@primer/css](https://github.com/primer/css) from 12.6.0 to 12.7.0.
- [Release notes](https://github.com/primer/css/releases)
- [Changelog](https://github.com/primer/css/blob/master/CHANGELOG.md)
- [Commits](https://github.com/primer/css/compare/v12.6.0...v12.7.0

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [mixin-deep](https://github.com/jonschlinkert/mixin-deep) from 1.3.1 to 1.3.2. **This update includes a security fix.**
- [Release notes](https://github.com/jonschlinkert/mixin-deep/releases)
- [Commits](https://github.com/jonschlinkert/mixin-deep/compare/1.3.1...1.3.2

)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Restrict navigation to display only direct children.

This reverts commit 8ac545a5.

This reverts commit c282e4b0.

Separating new PR from #188, since indpendent.

The current default is that when a grandparent is selected, the links to its
children *and all its grandchildren* are displayed in the navigation menu.
Setting `grandchildren_branch: true` in `_config.yml` delays the display of links
to grandchildren until their parent is selected.

Automatically replaces the title with a logo

A `navigation-list-child-list` is not displayed unless the enclosing `navigation-list-item` is `active`, so it needs to be generated only when `page.url == node.url or page.parent == node.title or page.grand_parent == node.title`.

(cherry picked from commit 97d1c663ef566ffe20fb1ec217fd2d8c1a8a2382)

(cherry picked from commit 468bf8368783309e69fdcaa91f7eb5b1e05d96aa)

(cherry picked from commit 2a5c38907488b998af75e9a1ef2499428b8f1a78)

Deduplicated anchor heading svg,
Anchor heading svg is now centered for heading

Using `index.md` as name for the parent page within a section allows lazy developers
to skip defining `permalink`. This is already working and this PR just updates the documentation.

v0.2.6 release