Fix docs: Add clarification for `cellData` in `dt-init columns.createdCell`

* Based on discussion in thre 22009
Fix: `dt-init createdCell` cellData prarameter now passes in the original data for the cell

* This reverts the last commit which documented the old behaviour.
  Thinking again about it, if you want to modify the rendered data use
  `$(cell).html()`.
Fix: If filtering data is null, undefined or NaN it is not included in the filter
DataTables 1.10.1 release