This function snaps a point to a line based on the
minimum distance between the point and the line
Usage
pointOnLine(cool, coop)
Value
A 4-length vector, with 'x','y' [coordinates of the point snapped to
the line], 'd' [distance from the input point to the new snapped
point], and 'chain' [accumulated along-line distance from the starting
of the line to the snapped point]