[Feature request] Add Markdown support

[5kull]

Using markdown in the description field would be awesome or at list support of clickable links.

[mrvladus]

It would mean that I need to embed full-blown markdown editor inside. I'll see if I can use other GTK projects for this, but if not - then I don't think I can implement that.

[5kull]

If not Markdown, is it possible to make URLs and URIs clickable?

Very often we need to have some kind of reference links for current tasks.

[mrvladus]

Something like this: #339 (comment)

I can't make links clickable inside TextView but in markdown preview it's possible. That was easier to implement than I thought :) It will be available in the new C version of Errands.

[5kull]

Cool, thank you very much!