Previous Card functionality

[iamsureshraju]

This project is awesome. Could you please add a "Previous Card" button functionality, so that we can go back on the cards learnt.

[jwasham]

You're right, I don't think there's a place to look at the cards you've learned. I honestly don't remember, it's been years since I've looked at this.
I won't be adding it myself, but if anyone wants to give it a try, I'm open to looking at the pull request.

[marielledoenges]

Hi! I will take this on. An open source contribution is required for one of my classes, so I will try to implement this feature.