Toolbar icon or keyboard shortcut to toggle Normal/Markdown in one action

[josephernest]

Clicking on the Settings button + Clicking on Show Markdown is a bit long...

It would be interesting to toggle Normal / Markdown in only one action. (Then it would be closer to StackEdit that even displays both Markdown on left / rendered result on the right)

What do you think about adding a toolbar icon near Settings button to toggle Markdown?

Or let's add a keyboard shortcut to quickly change this?

[JohnMcLear]

Welcome to see this as a pull request, I don't need to work on this. Anyone could do this, very low hanging fruit.