add support for SQL Server

Added Microsoft SQL Server support.
(Quite) tested on SQL Server 2008 only.

* Auto increment
Since mssql won't accept autoincrement null values in the insert statement, I added an `if` clause to `bindInsert` to ignore autoincrement columns if `AutoIncrBindValue()` is an empty string.

* Truncate
I used "delete from" without `where` clause, as `truncate` itself has only been introduced in SQL Server 2012.

Not implemented (yet?):
* `CreateTablesIfNotExists()`