Implemented skirt

lib/Slic3r/Layer.pm

@@ -46,6 +46,13 @@ has 'perimeters' => (
     default => sub { [] },
 );
 
+# ordered collection of extrusion paths to build skirt loops
+has 'skirts' => (
+    is      => 'rw',
+    isa     => 'ArrayRef[Slic3r::ExtrusionPath]',
+    default => sub { [] },
+);
+
 # collection of surfaces generated by offsetting the innermost perimeter(s)
 # they represent boundaries of areas to fill
 has 'fill_surfaces' => (