Move Point ctor into .cc file to hide shadowing from users

See #15 and #31.

poly2tri/common/shapes.cc

@@ -35,6 +35,10 @@
 
 namespace p2t {
 
+Point::Point(double x, double y) : x(x), y(y)
+{
+}
+
 std::ostream& operator<<(std::ostream& out, const Point& point) {
   return out << point.x << "," << point.y;
 }

poly2tri/common/shapes.h

@@ -57,7 +57,7 @@ struct Point {
   std::vector<Edge*> edge_list;
 
   /// Construct using coordinates.
-  Point(double x, double y) : x(x), y(y) {}
+  Point(double x, double y);
 
   /// Set this point to all zeros.
   void set_zero()