A "Dot Swap" tool. It just trades the positions of two dots on a
stuntsheet. Useful when moving points around to solve collisions - this
saves some of the time that would normally be used to drag and drop.
From Sean Parent: 'No Naked For Loops'; ie, whenever possible try to use algorithms.
Looks like we are trying to use a rotate here, so create a vector of indices, a vector of positions, then rotate the positions.  Accomplishes the same thing and is a little clearer.
Merge pull request #82 from calband/DotSwap

Dot Swap Tool