Added unit test for built-in cell functions.
Added unit test for built-in cell functions.

For now, I only test for function categories and their order in
each category.  But in the future I might test for argument types
as well.

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core