Refactor some parts of the Architecture:

* JSON visitor are located in the format namespace
  * Visitor are *real* visitor
  * Visitable class has been renamed to Object
  * Due to a bug in Visual Studio 2015, we move to VS2017

api/python/ELF/objects/pyHeader.cpp

@@ -18,7 +18,7 @@
 
 #include "pyELF.hpp"
 
-#include "LIEF/visitors/Hash.hpp"
+#include "LIEF/ELF/hash.hpp"
 #include "LIEF/ELF/Header.hpp"
 
 template<class T>
@@ -32,9 +32,8 @@ void init_ELF_Header_class(py::module& m) {
   //
   // Header object
   //
-  py::class_<Header>(m, "Header")
+  py::class_<Header, LIEF::Object>(m, "Header")
     .def(py::init<>())
-    .def(py::init<const std::vector<uint8_t>&>())
 
     .def_property("identity_class",
         static_cast<getter_t<ELF_CLASS>>(&Header::identity_class),
@@ -160,7 +159,7 @@ void init_ELF_Header_class(py::module& m) {
     .def("__ne__", &Header::operator!=)
     .def("__hash__",
         [] (const Header& header) {
-          return LIEF::Hash::hash(header);
+          return Hash::hash(header);
         })
 
     .def("__contains__",