As dict no column name

I propose that we modify pymssql to use a column name of `"(No column name)"` when the user uses `as_dict=True` and then does a query which returns output columns that are not named -- e.g.:

```sql
SELECT MAX(x) FROM (VALUES (1), (2), (3)) AS foo(x)
```

Currently, we don't add the column to the result row if it has no name. This confuses people.

I chose `"(No column name)"` because this is what SQL Server Management Studio uses.