Implement statements and transactions, fix return types.

[devonbessemer]

I accomplished three fixes while working with your library, figured they would be useful to pull:

• Implement statement, affectingStatement and unprepared methods
• Fix the return types for insert, update, and delete (statement returns bool, affectingStatement returns int)
• Implement basic transaction support: beginTransaction, commit, rollBack, and transactionLevel methods.

[devonbessemer]

Closed in favor of #27