Added reminder to NEWS for those that retort about := with 'just use matrix'.
Added reminder to NEWS for those that retort about := with 'just use matrix'.

Rdatatable/data.table,vlulla/data.table,vlulla/data.table,jangorecki/data.table,jangorecki/data.table,Rdatatable/data.table,jangorecki/data.table,Rdatatable/data.table,Rdatatable/data.table,vlulla/data.table,vlulla/data.table,jangorecki/data.table