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

xs/src/Polyline.cpp

@@ -0,0 +1,15 @@
+#include "Polyline.hpp"
+
+namespace Slic3r {
+
+Lines
+Polyline::lines()
+{
+    Lines lines;
+    for (int i = 0; i < this->points.size()-1; i++) {
+        lines.push_back(Line(this->points[i], this->points[i+1]));
+    }
+    return lines;
+}
+
+}