[HOTFIX] - Implement better handling of LIMIT/OFFSET in MSSQL driver

[joshmcrae]

This PR updates Table and Mssql with special behaviour for the MSSQL driver to address #44.

Problem

MSSQL has multiple ways of selecting a limited number of rows.

• SELECT TOP n [columns] FROM... where OFFSET and ORDER BY can be omitted
• OFFSET n FETCH NEXT r ROWS ONLY where both an offset and limit must be specified

The OFFSET clause can also be used without a limit, so long as an ORDER BY is specified.

Currently, queries that are generated where only a limit is specified break because an OFFSET clause isn't added.

Solution

The Table class adds a TOP n modifier to the selected columns list when only a limit is specified, without an offset. In cases where both an offset and limit are specified, the original behaviour remains with a no-op ORDER BY being added if missing.