Removing leading and trailing empty lines from all example files.

Using the following Perl script:
-----------------------------------------------------
#!/usr/bin/perl

local($/) = undef;
my $text = <>;

$text =~ s/\A\n+//mg;
$text =~ s/\n+\Z/\n/mg;

print "$text";
-----------------------------------------------------

Polygon/examples/Polygon/Example.cpp

@@ -1,4 +1,3 @@
-
 //-----------------------------------------------------------------------//
 // This is just a simple example that demonstrates how to use the
 // class CGAL::Polygon_2.
@@ -78,4 +77,3 @@ int main()
 
   return 0;
 }
-