expand markdown link support to include named links

[chadhs]

add support for markdown links that look like this:

[GeekDesk v3][]

and are later referenced by name like this:

[GeekDesk v3]: http://www.geekdesk.com/geekdesk-v3

[lacarmen]

This would be a change in markdown-clj, not Cryogen.

[chadhs]

Thanks for the heads up, i'll close this. @lacarmen I also noticed that it does work if you include the name like [this is a link][named link]. When the link text and named like match you can exclude the name. I'll report this to markdown-clj.

[chadhs]

yogthos/markdown-clj#69