Add Write methods to scene objects

Write methods are polymorphic, overridden by subclasses. There is a single operator<< for Objects that calls the right Write() method for the object. Neat.

src/object.cc

@@ -14,7 +14,7 @@
 #include "object.h"
 
 namespace charles {
-    
+
 #pragma mark - Objects
 
 /*
@@ -70,4 +70,21 @@ Object::SetMaterial(const Material& material)
     mMaterial = material;
 }
 
+
+void
+Object::Write(std::ostream& ost)
+    const
+{
+    ost << "[Object]";
+}
+
+
+std::ostream&
+operator<<(std::ostream& ost,
+           const Object& object)
+{
+    object.Write(ost);
+    return ost;
+}
+
 } /* namespace charles */