Option to use reference-style links

[EvitanRelta]

From the CommonMark spec: https://spec.commonmark.org/0.30/#reference-link

A reference link is in the form:

[foo][bar]

[bar]: /url "title"

But there's also different kinds of them: full, collapsed, and shortcut.
The above example is a full reference link. The other 2 are in the form:

[collapsed][]

[collapsed]: /url "title"

[shortcut]

[shortcut]: /url "title"