Markdown Reference Links should be supported

[Thraka]

My markdown reference link is rendering as plaintext instead of generating a link.

Reference links are formatted close to normal markdown links, but slightly different. Instead of a [link](https://....) a '[reference link][id of link]uses[ ]for the link portion instead of( )`.

Reference links are defined in a file through the following syntax:

[id of link]: https://github.com