K1 sliding Riser

This is a remix, but the the entire vent system has been redesigned. Instead of the circular vents (which are pretty cool), I went with a very simple sliding windows approach. It's easier to print, there are no parts to secure, and it's very robust. It uses the same corner pieces, which means the ends have round slots. The round slots need supports, I find printing the slot flat works best with minimal supports on the ends, but the K1 is not big enough. I've been thinking it might be easier to extend the corner pieces so that the sides (the slot and slide) can sit flat in the K1. Of course that would reduce the size of the vents, there are always tradeoffs.