added tracking of cards created

Hi muflax! Philip at Beeminder here. 

I've added a 3rd goal type, to track cards created. This has been really useful in forcing me to find facts that I can add to my anki decks. Thanks so much for doing the initial integration.

Codewise, it's a straight copy-paste of your other goal type. So there's almost certainly a better version that would count facts rather than cards, for example. But this has been working well for me since April 2013, and I finally got around to uploading it... thanks to my do-more-hacking goal.

Looks as though you're on hiatus; let us know if we can help when you're ramping back up.

Thanks again for making Anki part of my almost-daily routine. 

Philip