Add support for batched DML statements. Add tests for MultiplePreparedInsertStatements.

I have a special use case where there will always be two sequential inserts into separate tables. In order to minimise service time it would be better to do this in one call to the db.

This fork builds on the existing implementation of the prepared() method to add support for simple batched DML statements. The code could use some refactoring to reduce size, but it is largely functional not complicated.