Support clickable links in editor mode

(feature request)

I've been using macdown for years now. Thanks for building it.

I'd like to add a small feature, with your blessing, @uranusjr.

I often write documents with `[links like this](http://foo.com)`. They're clickable in preview mode of course, but not in editor mode.

It would be useful to me if I could click on them as links even in editor mode, perhaps only when combined with a keyboard key like control/cmd. IDEs support clickable links in code so this feels very familiar and expected to me, and I hope to others.

* Do you think this feature is a good idea?
* What files/classes/modules should I look at to get started?