Add method to register cell class for object class. Update example project to use new method.
Add documentation for the new `-registerCellClass:forObjectsWithClass:` method.
Update the README to reflect the new method.
Add a line to the README about not needing to write any data source methods.
Merge pull request #3 from ElectricPeelSoftware/register-cell-class

Provide and set up cells automatically