time_rename: Renames the columns in a data.table so that they end in '_t_0'
Description
This will rename the columns in a data.table so that
they end in '_t_0', which will be needed when folding the data.table. If
any of the columns already ends in '_t_0', a warning will be issued and
no further operation will be done. There is no need to use this function
to learn a DBN unless some operation with the variable names wants to be
done prior to folding a dataset.