Prusa i3 improved X ends for brass TR8 / T8 nuts (anti-backlash nuts supported)

With these modified X-ends (compatible with the [Prusa i3 improved XZ axis](https://www.thingiverse.com/thing:372056/) from [jkoljo](https://www.thingiverse.com/jkoljo)) you can use your favorite TR8 (sometimes called T8) acme lead screws + nuts on your Prusa i3 or RepRap. :)

I have made 4 versions of both X-ends. The differences:
- designed for normal TR8 nut / designed for anti-backlash TR8 nut
- **different ways of mounting the nut:**
- M3 screws and nuts
- screwing M3 directly int