Add relocation in the Abstract layer

The abstracted attributes are:
  * Address: virtual address where the relocation occurs
  * Size: size in bits of the relocation

See: LIEF::Relocation / lief.Relocation and abstract_reader

Resolve: #53

api/python/Abstract/init.cpp

@@ -23,4 +23,5 @@ void init_LIEF_module(py::module& m) {
   init_LIEF_Section_class(m);
   init_LIEF_Symbol_class(m);
   init_LIEF_Parser_class(m);
+  init_LIEF_Relocation_class(m);
 }