Ported (and used) ExtrusionPath->first_point

xs/src/ExtrusionEntity.cpp

@@ -8,6 +8,12 @@ ExtrusionPath::reverse()
     this->polyline.reverse();
 }
 
+const Point*
+ExtrusionPath::first_point() const
+{
+    return &(this->polyline.points.front());
+}
+
 ExtrusionPath*
 ExtrusionLoop::split_at_index(int index)
 {

xs/src/ExtrusionEntity.hpp

@@ -38,6 +38,7 @@ class ExtrusionPath : public ExtrusionEntity
     public:
     Polyline polyline;
     void reverse();
+    const Point* first_point() const;
 };
 
 class ExtrusionLoop : public ExtrusionEntity