Let Shift + Enter in markdown segments behave like Alt+G Alt+N

[heyarne]

Hi! First of all, great that you revived gorilla notebook. Very excited to see what this will develop into! I ran into something that's a minor annoyance for me and I thought I'd share, maybe this is helpful feedback for you. I'm running the notebooks in latest Firefox on Arch Linux.

Expected behavior

I expected Shift + Enter to render and exit a markdown segment. I also expected it to add a new cell below so the notebook can continue seamlessly.

Actual behavior

Nothing happens.

Environment & Version information

gorilla-notebook version

0.4.9