Ported Polygon->is_counter_clockwise() and rearranged code in .cpp files

xs/src/ExtrusionEntity.cpp

@@ -0,0 +1,32 @@
+#include "ExtrusionEntity.hpp"
+
+namespace Slic3r {
+
+void
+ExtrusionPath::reverse()
+{
+    this->polyline.reverse();
+}
+
+ExtrusionPath*
+ExtrusionLoop::split_at_index(int index)
+{
+    Polyline* poly = this->polygon.split_at_index(index);
+    
+    ExtrusionPath* path = new ExtrusionPath();
+    path->polyline      = *poly;
+    path->role          = this->role;
+    path->height        = this->height;
+    path->flow_spacing  = this->flow_spacing;
+    
+    delete poly;
+    return path;
+}
+
+ExtrusionPath*
+ExtrusionLoop::split_at_first_point()
+{
+    return this->split_at_index(0);
+}
+
+}