Inline variable insertion in markdown

[agoose77]

I'm now no longer iterating further on this concept, because I think it's reached a point where we have a good base implementation to use as a reference in discussions.

I’m convinced that this is a must-have for Jupyter, and (as outlined above) I think we need bigger discussions to address the next steps. I’d like to quickly say a big thank-you to all the contributors here for some interesting ideas and observations.

I don’t really know how best to take the next steps with this idea. I’m going to present it at the community call on Tuesday, so perhaps some ideas will come from that discussion.