Initialize the Status object with three parameters which describe the
Status#is checks for equality between two links, paying attention to whether the graph is
directed. Links are equal if they point to the same objects.
Status#indexOf checks if the link is in the register, find and return its first index in the link array.
Otherwise return -1.
Status#has is a convenience function.
Status#count returns a count of the number of times a link appears in the
force.links() array. It will always iterate through the whole array.