Define close_ls(), close_lseg(), lseg_length().
Write real code for close_sb(), close_pb(), inter_sb(), inter_lb().
Repair lseg_perp() which determines if two lsegs are perpendicular.
Repair lseg_dt() distance between two lsegs.
Note: close_sl() is clearly broken  but will repair later
 (calculating point on lseg rather than point on line).