The `Tangle` source would create a point field generically named
`nodevar`. This name was not indicitive of the data or its source. Thus,
the output point field has been renamed `tangle`.
The `Tangle` source was also creating a cell field (named `cellvar`).
This field was really just a mirror of the cell indices (counting from 0
on up). This field has been removed from the input. If you want such a
field, you can now use the `GenerateIds` filter to add it to any data
set.