minor changes
extension methods and cleanups

- ADD: ThrowIfNull extension method
- CVG: code cleanups
extension and helper methods

- ADD: FromDbValue() helper / extension methods
- ADD: ToDbValue() helper / extension methods
extension / helper methods

- ADD: Build() extension / helper methods
- ADD: BuildAll() extension / helper methods
- ADD: GetBytes() extension / helper methods
added ExecuteEnumerable() extension / helper methods