Statement and transaction support, various enhancements

[devonbessemer]

I created a new branch to pull from as I intend to continue enhancing/supporting the master branch at https://github.com/devonblzx/wp-eloquent. With this, I accomplished three primary 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.