Added phpdoc comments and rewrote classes

Changes:
+Now with 150% more phpdoc comments. 
+Redid the polygonal_chain class. 
--Rewrote constructor: 
  +It now takes an array of line segments as the parameter,
   which is kinda more in rhythm with how the other functions work.
--Changed naming conventions
  +Removed "vertices,"
   a polygonal_chain no longer has a vertices property,
   it has a line_segments property. The vertices are accessible
   through iteration.
--Implemented iterator interface:
  +Now the line segments may be looped through using foreach
+Introduced a poorly wrote __toString( ) function for line_segments