added documentation about non-normalized invalid dates
added documentation about non-normalized invalid dates

Change-Id: I88a95d8fac8af9085d41cf1b13c8ff3ee7abb141

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