add more quote types to markdown autopairs

[Axlefublr]

I believe this is quite a nice default, as various fancy quotes like “” ‘’ «» will appear in markdown more than anywhere.
Inserting a fancy quote and seeing it get autoclosed will spark the thought of “omg that's so nice!” — adding them to autopairs manually might simply be something most people won't think to do / won't care enough to do, while appreciating it as a default.
I was actually thinking to add those special quotes to all languages, but that's a lot more controversial; would love to hear thoughts about this.

[Axlefublr]

what sparked this idea is the fact that those quotes are understood by ms, mr, md