Add column aliasing support

Column aliasing is needed for Oracle paging ([pre 12c](http://www.oracle-base.com/articles/12c/row-limiting-clause-for-top-n-queries-12cr1.php) which finally offers sane syntax) when joining tables and returning columns from those tables with conflicting names.  Without aliasing you'll receive the usual `ambiguous column name` error on the wildcard select.

Here's is a simplified version from one of my projects where I join `FeedbackType` and `FeedbackStatus` to the `Feedback` table and return only the first page.  I built the `sqlPage` query using `SqlBuilder` and `Database.BuildPageQueries<Feedback>(...)`.  I plan to simplify this by improving `Database.SkipTake(...)` soon.

*Query call*
```
var data = Database.Query<Feedback, FeedbackType, FeedbackStatus>(sqlPage);
```

*Generated query*
```sql
SELECT * FROM (
    SELECT ROW_NUMBER() OVER (ORDER BY (SELECT NULL from dual)) peta_rn,
    peta_base.* FROM (
        SELECT
            f.id,
            f.title,
            ft.id as type_id,
            ft.name as type_name,
            fs.id as status_id,
            fs.name as status_name
        FROM Feedback f   
        INNER JOIN feedback_type ft ON ft.Id = f.feedback_type_id
        INNER JOIN feedback_status fs ON fs.Id = f.feedback_status_id) peta_base
) peta_paged
WHERE peta_rn>0 AND peta_rn<=10
ORDER BY peta_rn
```

*Pocos*
```c#
public class Feedback
{
        public int Id { get; set; }
        public string Title { get; set; }

        public FeedbackType Type { get; set; }
        public FeedbackStatus Status { get; set; }
}

public class FeedbackType
{
        [Alias("type_id")]
        public int Id { get; set; }
        [Alias("type_name")]
        public string Name { get; set; }
}

public class FeedbackStatus
{
        [Alias("status_id")]
        public int Id { get; set; }
        [Alias("status_name")]
        public string Name { get; set; }
}
```

I'm also trying to come up with a way to auto-prefix-alias all columns in a Poco, either with table attribute such as `[ColumnPrefixAlias("type_")]` or during query time.