Added mssql support

Issue #224

Caveats:
- MSSQL does not support timezone in the datetime2 db object, thus the time conversion tests are not  applicable under main_test.go TestTimeWithZone
- Added HasTop to all dialects, this indicates whether to use "Top" vs "Limit" and "Offset X Limit Y" vs "Offset X Row Fetch Next X Rows Only".  [scope_private.go].offsetSql(),  [scope_private.go].topSql() 

Let me know if there is anything I'm doing here that is glaringly wrong.