Special is now automatically set to true when a special card type is searched

I had some free time, and so I figured I'd work on a patch to resolve #16.

I added a SPECIAL_TYPES array to constants.py which contains the types that require special = True for gatherer to show card results. I then added a little check in get_filters() after the types array is created to check if the user asked for any special types, and if so, to set special = True.

I did verify ```mtg --type phenomenon``` now actually lists phenomena cards, so I believe this works.