Command for commenting or uncommeting selected text

[IgKh]

Based on a request made in #21:

Finally, more of a request if it makes sense for this editor. Please allow commenting selection. Either with a shortcut, right-click, or the file menu bar. This would toggle // of the selected lines.

[yavidor]

I think CTRL + / (I guess CMD + / in Mac) is a good idea (just tried to use this shortcut as an instinct from vscode and other editors, when I saw it doesn't work I wanted to add this as an issue and saw this)

[IgKh]

@yavidor Sure, makes sense.