Wrap partMeshNodal

**Is your feature request related to a problem? Please describe.**
@inducer thanks for this great work of wrapping metis. I am developer of the flood and tsunami package https://github.com/anuga-community/anuga_core and we use metis (indeed your pymetis wrapper) to partition our triangular mesh for mpi runs.

In the past for our python 2 version we used metis 4 and our own wrapper of the `partMeshNodal` procedure. When we moved to python 3 we decided to upgrade to using metis 5. Instead of writing our own wrapper we decided to use your wrapper, and your `pymetis.part_graph` procedure. Worked a charm.

But on closer examination the quality of our partitions (using `pymetis.part_graph`) and the scaling of our parallel code, it seems that the partitions produced by `pymetis.part_graph` are a little inferior to the partitions created by `partMeshNodal`. Our communication regions seem to be about 20% larger with `pymetis.part_graph`

**Describe the solution you'd like**
So I would like to request that you also add a wrapper to `partMeshNodal`

**Describe alternatives you've considered**
I did have a very short look at your wrapper code. I would be willing to try to code up the extension myself, but would appreciate any help from you.