title: cgal python intersection - trying to return a polygon more complex than a triangle
body: <p>I'd like to intersect two shapes, returning the overlap between the two. This has to include where the overlap is quite a complex shape (i.e. not just a triangle). Ultimately I want to do this in 3D but I'm running into the same issue even when I simplify this down to 2D that I can't get the resulting shape back as it doesn't match any of the basic "is_foo" template functions for 
  CGAL::Object. </p>
  
  <p>Code is below. Note the two triangles used should return an irregular quadrilateral of ((0.75, 0.0), (0.25, 0.0), (0.0, 1.0), (0.8, 0.2))</p>
  
  <pre><code>from CGAL.CGAL_Kernel import Point_2
  from CGAL.CGAL_Kernel import Triangle_2
  import CGAL.CGAL_Kernel as CGAL_Kernel
  
  tri1=Triangle_2( *[Point_2(*acoord) for acoord in [[0,0],[1,0],[0,1]] ] )
  tri2=Triangle_2( *[Point_2(*acoord) for acoord in [[1,1],[0.5,-1],[0,1]] ] ) 
  
  intersection=CGAL_Kernel.intersection(tri1,tri2)
  
  print(intersection.empty()) ### FALSE
  print(intersection.is_Point_2()) ### FALSE
  print(intersection.is_Triangle_2()) ### FALSE
  print(intersection.is_Segment_2()) ### FALSE
  print(intersection.is_Line_2()) ### FALSE
  print(intersection.is_Ray_2()) ### FALSE
  </code></pre>
  
  <p>Is there a way to get the quadrilateral out that I am not understanding? Am I approaching this the wrong way? Thanks in advance</p>