Add name to MPVariable binding for inspect and printing (#68)

Author: tbolender

ext/or-tools/math_opt.cpp

@@ -64,6 +64,7 @@ void init_math_opt(Rice::Module& m) {
 
   Rice::define_class_under<Variable>(mathopt, "Variable")
     .define_method("id", &Variable::id)
+    .define_method("name", &Variable::name)
     .define_method(
       "_eql?",
       [](Variable& self, Variable &other) {

test/math_opt_test.rb

@@ -74,4 +74,11 @@ def test_non_integer_solver
     end
     assert_equal "Glop does not support integer variables", error.message
   end
+
+  def test_variable_inspect
+    model = ORTools::MathOpt::Model.new("getting_started_lp")
+    var = model.add_integer_variable(-1.0, 1.5, "x")
+
+    assert_equal "x", var.inspect
+  end
 end