We're trying to avoid circular dependency errors.

This prevents false matches on relative links like
`[database](database.md)`.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14220

This filter will detect YAML Front Matter and convert it to an HTML
table for prettier formatting.

When `object_class.link_reference_pattern` was `nil` because object
being processed do not implemement link references `call` method
returned `nil` instead of returning document, even if document has been
processed in for basic reference pattern.

Closes https://dev.gitlab.org/gitlab/gitlabhq/issues/2660

Closes #2494

Closes #13625

Now that we're serving assets directly from the Gemojione gem's path,
the images are not in an `emoji/` sub-folder.

- Apply the RelativeLinkFilter filter to other formats, e.g.,
  reStructuredText so links from the Files view or the Project view work
- Remove the AsciidocPipeline pipeline

Fixes #3533.

Closes #11853

This allows for future pipelines to more easily define a custom
whitelist.

Closes #12517

Closes #6077

This reverts commit d337d5e7.

This reverts commit 4b027bc9.