Will not panic on interface type in struct. (#62)

* Will not panic on interface type in struct.

structs.go

@@ -550,6 +550,11 @@ func (s *Struct) nested(val reflect.Value) interface{} {
 		// TODO(arslan): should this be optional?
 		finalVal = val.Interface()
 	case reflect.Slice, reflect.Array:
+		if val.Type().Kind() == reflect.Interface {
+			finalVal = val.Interface()
+			break
+		}
+
 		// TODO(arslan): should this be optional?
 		// do not iterate of non struct types, just pass the value. Ie: []int,
 		// []string, co... We only iterate further if it's a struct.

structs_test.go

@@ -1362,3 +1362,17 @@ func TestNonStringerTagWithStringOption(t *testing.T) {
 		t.Errorf("Value for field Animal should not exist")
 	}
 }
+
+func TestMap_InterfaceValue(t *testing.T) {
+	type TestStruct struct {
+		A interface{}
+	}
+
+	expected := []byte("test value")
+
+	a := TestStruct{A: expected}
+	s := Map(a)
+	if !reflect.DeepEqual(s["A"], expected) {
+		t.Errorf("Value does not match expected: %q != %q", s["A"], expected)
+	}
+}