Move source to src.

src/portal.cpp

@@ -0,0 +1,11 @@
+// -*- C++ -*-
+
+#include "physics/vector.h"
+#include "portal.h"
+
+using namespace mbostock;
+
+Portal::Portal(const Vector& min, const Vector& max,
+               int room, int origin, bool reset)
+    : box_(min, max), room_(room), origin_(origin), reset_(reset) {
+}