implemented simple evaluator for program,

statements and integer literals, together with
tests

test/utils/test_eval.cpp

@@ -0,0 +1,10 @@
+#include "object/integers.hpp"
+#include "object/object.hpp"
+#include "utils.hpp"
+
+namespace test::utils {
+    void test_integer_object(object::object* obj, int expected) {
+        object::integer* i = cast<object::integer>(obj);
+        CHECK(i->value == expected);
+    }
+} // namespace test::utils