Improving TypeConverter implementation 

The TypeConverters were not correctly implementing the base TypeConverter class. 

I've updated them to better match the example implementations on [MSDN](http://msdn.microsoft.com/en-us/library/ayybcxe5.aspx) and tested them briefly. (This project will need proper DB unit testing set up) and they seem to work. 

I would recommend that a proper testing mechanism would be set up before releasing new updates though.