Introduced Command/RollbackTransaction methods.
Introduced the Transaction property.
Improved the Dispose metod.
Implemented the transaction methods.
Renamed SaveUnitOfWorkAttribute to CommitTransactionAttribute.
Addressed not using SaveAsync.
Removed the SaveAsync method.
Introduced the ExceptionFilterAttribute class.
Addressed AttributeUsage.
Implemented the OnExceptionAsync method.
Registered RollbackTransactionAttribute as global filter.
Merge pull request #32 from jwChung/improve-unit-of-work

Improve unit of work