Allow multiple documents opening

[camlafit]

hello

Could be nice to allow multiple opening feature, when we want open more than one document, we get only one markdown document.
Others documents are opened with default editor or preview feature.

Thanks

[12people]

It's worth noting that this wouldn't be useful just for multiple documents, but also for the same document open in multiple panes (which I personally use quite often).

[Blayr]

I'm using this for note-taking, and being able to use the WYSIWYG editor with more than one file or pane at a time would make my setup perfect.