Wild Update: Giant Shelf Mushrooms

Since the concept art for the Birch Forests in the Wildlife Update featured shelf mushrooms, I thought it would be cool if they could be enlarged like every other mushroom in the game.  They could either grow to the size of slabs on trees, or if they have enough space like on a cliffside they could get as big as brown mushrooms do!  It'd be a new and interesting way to make vertical paths.