Place the loop where you want your roundabout to be centered, then rotate the Straight or Diagonal exits to face any of the 8 possible directions and attach to the loop.
The chain signal placed between the exit points ensures that multiple trains can use the roundabout simultaneously so long as their paths don't need to overlap.
Just added 45 degree bypasses. Previously if you needed to make a 45 degree right turn, the train would have to cross over its own path. Long trains would have been able to collide with themselves.
Example image: https://imgur.com/a/y1G8f