Adding get_requires() to Python bindings (#1019)

This is a requirement from the Math Proof Generation Team of $Piˆ2$ to
get easy access to the Pattern of a requires clause.

This PR must be merged before this [PyK
PR](runtimeverification/pyk#1056) that will
properly expose this binding to the Pi2 project.

bindings/python/ast.cpp

@@ -179,7 +179,8 @@ void bind_ast(py::module_ &m) {
           py::arg("is_claim") = false)
       .def_property_readonly("is_claim", &kore_axiom_declaration::is_claim)
       .def("add_pattern", &kore_axiom_declaration::add_pattern)
-      .def_property_readonly("pattern", &kore_axiom_declaration::get_pattern);
+      .def_property_readonly("pattern", &kore_axiom_declaration::get_pattern)
+      .def_property_readonly("requires", &kore_axiom_declaration::get_requires);
 
   py::class_<
       kore_module_import_declaration,