Implement type checking for XS objects

Type handling is mainly done using templates.
Template Slic3r::ClassTraits is used to store info about exported types (perl class name). Currently only perl class name and refference name is used.
Template values are initialized by REGISTER_CLASS macro. This macro is used in .cpp file of class ( it needs to be used exactly for each type).

Ref<type> class is used to return value as perl reference. Operator overloading is used to make c++ and XSpp happy, only pointer value should be possible to return.

Clone<type> class is used to return copy of value ( using new and copy constructor). Copy is created on assigment, this should be probably improved (memory leak on multiple assignments).
It is overloaded to be able to return type, type* and type&.

Typechecking in ExtrusionEntityCollection updated to check all passed types.

xs/src/Flow.cpp

@@ -1,5 +1,8 @@
 #include "Flow.hpp"
 #include <cmath>
+#ifdef SLIC3RXS
+#include "perlglue.hpp"
+#endif
 
 namespace Slic3r {
 
@@ -112,4 +115,8 @@ Flow::_spacing(float width, float nozzle_diameter, float height, float bridge_fl
     return width - OVERLAP_FACTOR * (width - min_flow_spacing);
 }
 
+#ifdef SLIC3RXS
+REGISTER_CLASS(Flow, "Flow");
+#endif
+
 }