Auto pair markdown symbols

[nixsee]

It would be very nice if when you type ** for bold, it creates the paired ** and automatically puts the cursor in between. Same for * italics, and any other paired symbols. The problem is that the editor shows **xyz as bolded, but the Preview does not because it is not proper markdown syntax.

You already have this function for [, [[, etc... so I hope this isn't too big of a job!