Beginning Centipede construction

Attempting to use a factory method to create the Centipede. Problems:
lots of private Centipede members will leak from accessor use; need to
figure out how to create Points based on the head location (for the
purpose of creating other segments)
some comments and style
building segment locations from head point

assuming we are building a centipede whose head is at the left and the
tail extends to the right.