Make `code` elements in links display as such

When a link consisted only of an inline code block -- ```[`like this`](https://google.com/)``` -- it was hard to tell that it was even a link.

Before:

> ![Screen_Shot_2015-07-31_at_5.45.06_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/eda0a0630024d461c8de151d06e9f4db/Screen_Shot_2015-07-31_at_5.45.06_PM.png)

After:

> ![Screen_Shot_2015-07-31_at_5.43.15_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/9542c49cfb4d43c015d464ef0ba0440f/Screen_Shot_2015-07-31_at_5.43.15_PM.png)


See merge request !1082