Also adds the ability to run rspecs with relative_url_defined on the enviornment. For example:

RELATIVE_URL_ROOT=/gitlab rspec

Closes #1728

These helpers are no longer dependent on the current user state. Hooray!

There wasn't really a reason to have them as a constant, and we were
getting "already defined" warnings which are always annoying.

This module is now the sole source of knowledge for *how* we render
Markdown (and GFM).

It was redundant because `gfm` also took options.

The patches reduces pressure on GC and reduces markdown processing time

When this option is `:description`, we use a more restrictive whitelist.
This is used for Project and Group description fields.

Forces a `rel="nofollow"` attribute on all external links.

Instead of using a fork, we subclass the filter and only apply the
`task-list` class to list items that actually are task lists.

Closes #1645

See https://github.com/github/task_list/pull/60

This just extends the HTML::Pipeline::SanitizationFilter with our custom
whitelist.

Removes header and table of contents processing from Redcarpet renderer.

Removes emoji-centric tests from GFM specs 

Commit ranges, commits, external issues, issues, labels, merge requests,
snippets, users.

Extract and re-insert links after sanitizing user markup.