A gardener is putting up a straight fence. It starts at start metres and ends at end metres, and it is split into sections equal sections.
Every section needs a post at each end, and neighbouring sections share a post. So there is a post at the very start, a post at the very end, and posts in between.
Task: write post_positions(start, end, sections) and return the position of every post, in metres, as a plain list, going from start to end.
sections is always at least 1.start can be bigger than end. Then the positions go down from start to end.